Seed Setting Rate Research Articles

Temporal and spatial variation in the direct and indirect effects of climate on reproduction in alpine populations of Ranunculus acris L

AbstractPlant reproduction in alpine environments is affected by climate both directly through climate impacts on growth and phenology, and indirectly through impacts on the biotic interactions affecting pollination success. These effects can be highly variable in time and space. In this study we investigated how different abiotic and biotic factors influence reproductive investment and success in populations of Ranunculus acris across an alpine landscape over a two-year period. In an alpine area at Finse, southern Norway, we measured reproductive investment (total seed mass) and reproductive success (seed-set rate) in 38 sites differing in temperature (related to elevation) and length of the growing season (related to time of snowmelt). To assess biotic interactions, we measured floral density and pollinator visits and conducted a supplemental pollen experiment. Reproductive investment and success increased with temperature, but only when floral density and/or number of pollinator visits was high, and only in the warmer year (2016). Reproduction in R. acris was pollen-limited in both years, especially at warmer temperature and in sites with early snowmelt. Pollinator visits increased with temperature and with higher floral density, suggesting a shift in relative importance of the biotic factors (from plants to pollinators) in limiting reproduction with increasing temperature. Our study shows that reproductive investment and success in R. acris is affected by climate through the interactive effects of abiotic and biotic processes. These effects vary between years and across the landscape, suggesting a potential for larger-scale buffering of climate change effects in heterogeneous landscapes.

Genome-wide and functional analysis of late embryogenesis abundant (LEA) genes during dormancy and sprouting periods of kernel consumption apricots (P. armeniaca L. × P. sibirica L.)

Late embryogenesis abundant (LEA) proteins play a crucial role in protecting cells from stress, making them potential contributors to abiotic stress tolerance. This study focuses on apricot (P. armeniaca L. × P. sibirica L.), where a comprehensive genome-wide analysis identified 54 LEA genes, categorized into eight subgroups based on phylogenetic relationships. Synteny analysis revealed 14 collinear blocks containing LEA genes between P. armeniaca × P. sibirica and Arabidopsis thaliana, with an additional 9 collinear blocks identified between P. armeniaca × P. sibirica and poplar. Examination of gene structure and conserved motifs indicated that these subgroups exhibit consistent exon-intron patterns and shared motifs. The expansion and duplication of LEA genes in P. armeniaca × P. sibirica were driven by whole-genome duplication (WGD), segmental duplication, and tandem duplication events. Expression analysis, utilizing RNA-seq data and quantitative real-time RT-PCR (qRT-PCR), indicated induction of PasLEA2-20, PasLEA3-2, PasLEA6-1, Pasdehydrin-3, and Pasdehydrin-5 in flower buds during dormancy and sprouting phases. Coexpression network analysis linked LEA genes with 15 cold-resistance genes. Remarkably, during the four developmental stages of flower buds in P. armeniaca × P. sibirica - physiological dormancy, ecological dormancy, sprouting period, and germination stage - the expression patterns of all PasLEAs coexpressed with cold stress-related genes remained consistent. Protein-protein interaction networks, established using Arabidopsis orthologs, emphasized connections between PasLEA proteins and cold resistance pathways. Overexpression of certain LEA genes in yeast and Arabidopsis conferred advantages under cold stress, including increased pod length, reduced bolting time and flowering time, improved survival and seed setting rates, elevated proline accumulation, and enhanced antioxidative enzymatic activities. Furthermore, these overexpressed plants exhibited upregulation of genes related to flower development and cold resistance. The Y1H assay confirmed that PasGBF4 and PasDOF3.5 act as upstream regulatory factors by binding to the promoter region of PasLEA3-2. PasDOF2.4, PasDnaJ2, and PasAP2 were also found to bind to the promoter of Pasdehydrin-3, regulating the expression levels of downstream genes. This comprehensive study explores the evolutionary relationships among PasLEA genes, protein interactions, and functional analyses during various stages of dormancy and sprouting in P. armeniaca × P. sibirica. It offers potential targets for enhancing cold resistance and manipulating flower bud dormancy in this apricot hybrid.

The communities of arbuscular mycorrhizal fungi established by different winter green manures in paddy fields promote post-cropping rice production1

Winter planting green manures in southern China effectively improve soil properties and rice production through microbial community construction. However, the effects of soil communities of arbuscular mycorrhizal fungi (AMF) from different winter planting green manures on the soil properties and post-cropping rice production remain unclear. In this study, the soil AMF communities of three common winter planting patterns in Southern China, winter fallow, winter ryegrass (Lolium multiflorum L.), and winter Chinese milk vetch (Astragalus sinicus L.), were explored and their effects on post-cropping rice production were investigated. Compared with winter fallow, the winter ryegrass and winter Chinese milk vetch patterns could alleviate soil acidification, significantly increase soil AMF spore density, and improve the soil AMF community structure. Based on sterilized soil, rice production indicators such as thousand-seed weight, theoretical yield, and the grain amylose and total sugar contents of rice inoculated with AMF spores from winter Chinese milk vetch soil were 6.68-53.57% higher than those without AMF inoculation. Rice panicle weight, seed setting rate, and theoretical yield were 15.38-22.71% higher in the treatment with AMF spores from winter ryegrass soil than in the treatments with no AMF inoculation. In addition, the protein, amylose, and total sugar contents of rice grains were 14.92, 104.82, and 802.23 mg kg-1, respectively, which were 31.31, 14.25 and 34.47% higher than those without AMF inoculation. The AMF community dominated by Glomus and Acaulospora in winter Chinese milk vetch had a more positive effect on the improvement of rice yield, while the AMF community dominated by Glomus in winter ryegrass soil was more conducive to rice quality improvement. These findings have revealed the critical role of AMF communities from green manure in rice production, which lays the theoretical basis for a promising strategy to promote the sustainable development of southern winter agriculture.

Lectin Receptor-Like Protein Kinase OsNRFG6 is Required for Embryo Sac Development and Fertilization in Neo-Tetraploid Rice

Great yield-enhancing prospects of autotetraploid rice was restricted by various polyploidy-induced reproductive dysfunction. To surmount these challenges, our group has generated a series of valuable fertile tetraploid lines (denoted as neo-tetraploid rice) through 20-year efforts. With this context, a G-type lectin receptor-like kinase, OsNRFG6, was identified as a pivotal factor associated with reproductive regulation in neo-tetraploid rice. Nevertheless, it is still elusive about a comprehensive understanding of its precise functional roles and underlying molecular mechanisms during reproduction of neo-tetraploid rice. Here, we demonstrated that OsNRFG6 executed a constitutive expression pattern and encoded proteins localizing in perinucleus and endoplasmic reticulum. Subsequently, four independent mutant lines of OsNRFG6 within neo-tetraploid rice background were further identified, all displaying low seed-setting rate due to abortive embryo sacs and defective double fertilization. RNA-seq and RT-qPCR revealed a significant down-regulation of OsNRFG6 and female reproductive genes such as OsMEL1 and LOG in ovaries prior to and post-fertilization, attributing this effect to OsNRFG6 mutation. Furthermore, through yeast-two hybrids, bimolecular fluorescence complementation assays, and luciferase complementation imaging assays, it was determined that OsNRFG6 could interact with itself and two female reproductive proteins (LOG and OsDES1) to form protein complexes. These results elucidate the reproductive functions and molecular pathway governed by OsNRFG6 in regulating fertility of neo-tetraploid rice, offering insights into molecular understanding of fertility improvement in polyploid rice.

Nitrogen application increased yield sensitivity of indica hybrid rice to climate resource

Rice yield variability can be attributed to the range of sowing dates across extensive cropping areas and varying nitrogen application rates. Nonetheless, the precise quantitative relationship between sowing dates, nitrogen application rates, and rice yield development remains elusive. In this study, we evaluated differences in dry matter and yield components of three indica hybrid varieties for five sowing dates at four ecological sites in the middle and lower reaches of the Yangtze River, China in 2019 and 2020, with three nitrogen application rates. Results indicated that yield initially increased and then decreased with delayed sowing dates. Photosynthetically active radiation accumulation after anthesis (PARAA) was identified as the key positive climate resource affecting rice yield, decreasing by an average of 19.7 MJ m−2 for every 15-day delay in sowing. Nitrogen agronomic efficiency decreased linearly with the delay in sowing dates. Early sowing of rice with high PARAA and effective accumulated temperature after anthesis (EATAA) showed yield increases due to nitrogen application, whereas late-sown rice with insufficient photothermal resources did not exhibit marked yield improvement and may experience yield reduction. Ensuring adequate dry matter accumulation after anthesis and high seed setting rate was the main way to increase yield, influenced by sowing dates and nitrogen application rates. Intriguingly, our study revealed that nitrogen application markedly enhanced yield sensitivity to PARAA and EATAA. This finding underscores the pivotal role of nitrogen in modulating crop responsiveness to climate resources, and contributes to a deeper understanding of agronomic practices for optimizing yield under varying climatic conditions.

A Quadruple Mutant of OsPRP1 Controls Pollen Fertility by Regulating the Expression of Anther Development-Related Genes in Oryza sativa L.

Plant proline-rich proteins (PRPs) are cell wall proteins that are widely distributed in plants. Previous studies have shown that these proteins play a crucial role in adversity stress processes, but their function in the regulation of pollen fertility in rice remains unknown. In this study, we identified that OsPRP1 contains a Pollen_Ole-e_I allergenic structural domain, obtained the OsPRP1 quadruple mutant named osprp1.1/1.2/1.3/1.4, and observed significant reductions in pollen fertility, seed-setting rates, and the deformation and collapse of microspores during the late stages of pollen development. RNA-Seq analysis indicated the down-regulation of genes involved in anther development in osprp1.1/1.2/1.3/1.4, suggesting that OsPRP1 plays a role in regulating pollen fertility. In conclusion, a loss of function in OsPRP1.1/1.2/1.3/1.4 leads to decreased pollen fertility and seeding rates, which not only expands the functional spectrum of plant PRP genes but also provides new theoretical insight into the mechanism of fertility regulation in rice.

The receptor kinase OsANX limits precocious flowering and inflorescence over-branching and maintains pollen tube integrity in rice

CrRLK1L subfamily members are involved in diverse growth- and development-related processes in Arabidopsis. However, the functions of their counterparts in rice are unknown. Here, OsANX expression was detected in developing inflorescences, mature pollen grains, and growing pollen tubes, and it was localized to the plasma membrane in pollen grains and tobacco epidermal cells. Homozygous osanx progeny could not be segregated from the CRISPR/Cas9-edited mutants osanx-c1+/- and osanx-c2+/-, and such progeny were segregated only occasionally from osanx-c3+/-. Further, all three alleles showed osanx male but not female gamete transmission defects, in line with premature pollen tube rupture in osanx-c3. Additionally, osanx-c3 exhibited precocious flowering, excessively branched inflorescences, and an extremely low seed setting rate of 1.4 %, while osanx-c2+/- and osanx-c3+/- had no obvious defects in inflorescence development or the seed setting rate compared to wild-type Nipponbare (Nip). Consistent with this, the complemented line pPS1:OsANX-GFP/osanx-c2 (PSC), in which the lack of OsANX expression was inflorescence-specific, showed slightly earlier flowering and overly-branched panicles. Multiple inflorescence meristem transition-related and inflorescence architecture-related genes were expressed at higher levels in osanx-c3 than in Nip; thus, they may partially account for the aforementioned mutant phenotypes. Our findings broaden our understanding of the biological functions of OsANX in rice.

Ectopic expression of OsWOX9A alters leaf anatomy and plant architecture in rice.

Ectopic expression of OsWOX9A induces narrow adaxially rolled rice leaves with larger bulliform cells and fewer large veins, probably through regulating the expression of auxin-related and expansin genes. The WUSCHEL-related homeobox (WOX) family plays a pivotal role in plant development by regulating genes involved in various aspects of growth and differentiation. OsWOX9A (DWT1) has been linked to tiller growth, uniform plant growth, and flower meristem activity. However, its impact on leaf growth and development in rice has not been studied. In this study, we investigated the biological role of OsWOX9A in rice growth and development using transgenic plants. Overexpression of OsWOX9A conferred narrow adaxially rolled rice leaves and altered plant architecture. These plants exhibited larger bulliform cells and fewer larger veins compared to wild-type plants. OsWOX9A overexpression also reduced plant height, tiller number, and seed-setting rate. Comparative transcriptome analysis revealed several differentially expressed auxin-related and expansin genes in OsWOX9A overexpressing plants, consistent with their roles in leaf and plant development. These results indicate that the ectopic expression of OsWOX9A may have multiple effects on the development and growth of rice, providing a more comprehensive picture of how the WOX9 subfamily contributes to leaf development and plant architecture.

Morphological Study on the Differentiation of Flower Buds and the Embryological Stages of Male and Female Floral Organs in Lespedeza davurica (Laxm.) Schindl. cv. JinNong (Fabaceae).

Lespedeza davurica (Laxm.) is a leguminous plant with significant ecological benefits, but its embryonic development mechanism remains unclear. We investigated the flower bud differentiation, megaspore and microspore formation, gametophyte development, and embryo and endosperm development in L. davurica. Our aim was to elucidate the relationship between the external morphology and internal development processes of male and female floral organs during growth, as well as the reproductive factors influencing fruiting. The results indicated that although the pistil develops later than the stamen during flower bud differentiation, both organs mature synchronously before flowering. L. davurica pollen exhibits three germination grooves, a reticulate outer wall, and papillary structures on the anther surface. In vivo pollination experiments revealed abnormal spiral growth of L. davurica pollen tubes within the style and the occurrence of callus plugs, which may reduce the seed setting rate. The anther wall development follows the dicotyledonous type, with tetrads formed through microspore meiosis exhibiting both left-right symmetry and tetrahedral arrangements. L. davurica has a single ovule, and the embryo sac develops in the monosporic polygonum type. After dormancy, the zygote undergoes multiple divisions, progressing through spherical, heart-shaped, and torpedo-shaped embryo stages, culminating in a mature embryo. A mature seed comprises cotyledons, hypocotyl, embryo, radicle, and seed coat. Phylogenetic tree analysis reveals a close genetic relationship between L. davurica and other leguminous plants from the genera Lespedeza and Medicago. This study provides valuable insights into the regulation of flowering and hybrid breeding in leguminous plants and offers a new perspective on the development of floral organs and seed setting rates.

Bulked Segregant RNA-Seq Analysis of Pollinated Pistils Reveals Genes Influencing Spikelet Fertility in Rice

Prezygotic isolation is important for successful fertilization in rice, significantly affecting yield. This study focused on F5:6 generation plants derived from inter-subspecific crosses (Nipponbare × KDML105) with low (LS) and high seed-setting rates (HS), in which normal pollen fertility was observed. However, LS plants showed a reduced number of pollen grains adhering to the stigma and fewer pollen tubes reaching the ovules at 4‒5 h post-pollination, compared with HS plants. Bulked segregant RNA-Seq analysis of pollinated pistils from the HS and LS groups revealed 249 and 473 differentially expressed genes (DEGs), respectively. Kyoto Encyclopedia of Genes and Genomes analysis of the HS and LS- specific DEGs indicated enrichment in metabolic pathways, pentose and glucuronate interconversions, and flavonoid biosynthesis. Several of these DEGs exhibited co-expression with pollen development genes and formed extensive clusters of co-expression networks. Compared with LS pistils, enzyme genes controlling pectin degradation, such as OsPME35 and OsPLL9, showed similar expression patterns, with higher levels in HS pistils pre-pollination. Os02g0467600, similar to cinnamate 4-hydroxylase gene (CYP73), involved in flavonoid biosynthesis, displayed higher expression in HS pistils post-pollination. Our findings suggest that OsPME35, OsPLL9, and Os02g0467600 contribute to prezygotic isolation by potentially modifying the stigma cell wall (OsPME35 and OsPLL9) and controlling later processes such as pollen-stigma adhesion (Os02g0467600) genes. Furthermore, several DEGs specific to HS and LS were co-localized with QTLs and functional genes associated with spikelet fertility. These findings provide valuable insights for further research on rice spikelet fertility, ultimately contributing to the development of high-yielding rice varieties.

Cytological Observation and RNA-Seq Analyses Reveal miR9564 and Its Target Associated with Pollen Sterility in Autotetraploid Rice.

Understanding the regulation of autotetraploid sterility is essential for harnessing the strong advantages in genomic buffer capacity, biodiversity, and heterosis of autotetraploid rice. miRNAs play crucial roles in fertility regulation, yet information about their reproductive roles and target genes in tetraploid rice remains limited. Here, we used three tetraploid lines, H1 (fertile), HF (fertile), and LF (sterile), to investigate cytological features and identify factors associated with autotetraploid sterility. LF showed abnormal meiosis, resulting in low pollen fertility and viability, ultimately leading to scarce fertilization and a low-seed setting compared to H1 and HF. RNA-seq revealed 30 miRNA-candidate target pairs related to autotetraploid pollen sterility. These pairs showed opposite expression patterns, with differential expression between fertile lines (H1 and HF) and the sterile line (LF). qRT-PCR confirmed that miR9564, miR528, and miR27874 were highly expressed in the anthers of H1 and HF but not in LF, while opposite results were obtained in their targets (ARPS, M2T, and OsRPC53). Haplotype and expression pattern analyses revealed that ARPS was specifically expressed in lines with the same haplotype of MIR9564 (the precursor of miR9564) as LF. Furthermore, the Dual-GFP assay verified that miR9564 inhibited the fluorescence signal of ARPS-GFP. The over-expression of ARPS significantly decreased the seed setting rate (59.10%) and pollen fertility (50.44%) of neo-tetraploid rice, suggesting that ARPS plays important roles in autotetraploid pollen sterility. This study provides insights into the cytological characteristic and miRNA expression profiles of tetraploid lines with different fertility, shedding light on the role of miRNAs in polyploid rice.

Physicochemical Properties and Fine Structure of Starch in Jinong Xiangruan 1 and DGR1 Soft Rice Varieties Cultivated in Different Regions of China

Rice, a staple food for billions around the globe, is cultivated in numerous forms. Among them, soft rice is well known, which is characterized by its tender, creamy consistency and desirable texture. In this study, we examined the physicochemical properties and fine structure of starch from two soft rice varieties, Jinong Xiangruan 1 and DGR1, cultivated in different regions in China (Baodi District, Tianjin City; Liaoning Province; and Fengyang City, Anhui Province). The aim was to understand how amylopectin content (AC) influences rice quality. This research aims to bridge the knowledge gap regarding the role of amylopectin in determining rice’s adhesive consistency and viscosity. Significant regional differences were observed in yield components such as the number of grains per panicle, seed setting rates and 1000-grain weight, with Liaoning generally showing higher performance metrics compared to other regions. Physicochemical analysis highlighted that though glue consistency and taste values showed little regional variation, AC significantly influenced rice hardness and viscosity. Rapid Visco Analyzer (RVA) profile analysis further demonstrated distinct differences in viscosity characteristics, underscoring the regional impacts on starch behavior. Additionally, molecular weight distribution and amylopectin chain length analysis, conducted via SEC-MALLS-RI and ICS ion chromatography, revealed notable differences in starch composition across varieties and locations. The findings suggest that environmental conditions play a crucial role in defining starch characteristics and, consequently, the eating quality of rice. This provides valuable insights for breeding high-quality japonica rice with broad adaptability.

MORN motif-containing protein OsMORN1 and OsMORN2 are crucial for rice pollen viability and cold tolerance.

The pollen viability directly affects the pollination process and the ultimate grain yield of rice. Here, we identified that the MORN motif-containing proteins, OsMORN1 and OsMORN2, had a crucial role in maintaining pollen fertility. Compared with the wild type (WT), the pollen viability of the osmorn1 and osmorn2 mutants was reduced, and pollen germination was abnormal, resulting in significantly lower spikelet fertility, seed-setting rate, and grain yield per plant. Further investigation revealed that OsMORN1 was localized to the Golgi apparatus and lipid droplets. Lipids associated with pollen viability underwent alterations in osmorn mutants, such as the diacylglyceride (18:3_18:3) was 5.1-fold higher and digalactosyldiacylglycerol (18:2_18:2) was 5.2-fold lower in osmorn1, while the triacylglycerol (TG) (16:0_18:2_18:3) was 8.3-fold higher and TG (16:0_18:1_18:3) was 8.5-fold lower in osmorn2 than those in WT. Furthermore, the OsMORN1/2 was found to be associated with rice cold tolerance, as osmorn1 and osmorn2 mutants were more sensitive to chilling stress than WT. The mutants displayed increased hydrogen peroxide accumulation, reduced antioxidant enzyme activities, elevated malondialdehyde content, and a significantly decreased seedling survival rate. Lipidomics analysis revealed distinct alterations in lipids under low temperature, highlighting significant changes in TG (18:2_18:3_18:3) and TG (18:4_18:2_18:2) in osmorn1, TG (16:0_18:2_18:2) and PI (17:2_18:3) in osmorn2 compared to the WT. Therefore, it suggested that OsMORN1 and OsMORN2 regulate both pollen viability and cold tolerance through maintaining lipid homeostasis.

Seed germination demonstrates inter-annual variations in alkaline tolerance: a case study in perennial Leymus chinensis

Background and aimsThe escalating issue of soil saline-alkalization poses a growing global challenge. Leymus chinensis is a perennial grass species commonly used in the establishment and renewal of artificial grasslands that is relatively tolerant of saline, alkaline, and drought conditions. Nonetheless, reduced seed setting rates limit its propagation, especially on alkali-degraded grassland. Inter-annual variations have an important effect on seed yield and germination under abiotic stress, and we therefore examined the effect of planting year on seed yield components of L. chinensis.MethodsWe grew transplanted L. chinensis seedlings in pots for two (Y2), three (Y3), or four (Y4) years and collected spikes for measurement of seed yield components, including spike length, seed setting rate, grain number per spike, and thousand seed weight. We then collected seeds produced by plants from different planting years and subjected them to alkaline stress (25 mM Na2CO3) for measurement of germination percentage and seedling growth.ResultsThe seed setting rate of L. chinensis decreased with an increasing number of years in pot cultivation, but seed weight increased. Y2 plants had a higher seed setting rate and more grains per spike, whereas Y4 plants had a higher thousand seed weight. The effects of alkaline stress (25 mM Na2CO3) on seed germination were less pronounced for the heavier seeds produced by Y4 plants. Na2CO3 caused a 9.2% reduction in shoot length for seedlings derived from Y4 seeds but a 22.3% increase in shoot length for seedlings derived from Y3 seeds.ConclusionsOur findings demonstrate significant differences in seed yield components among three planting years of L. chinensis under pot cultivation in a finite space. Inter-annual variation in seed set may provide advantages to plants. Increased alkalinity tolerance of seed germination was observed for seeds produced in successive planting years.

Transcription factor OsSHR2 regulates rice architecture and yield per plant in response to nitrogen.

Mutation of OsSHR2 adversely impacted root and shoot growth and impaired plant response to N conditions, further reducing the yield per plant. Nitrogen (N) is a crucial factor that regulates the plant architecture. There is still a lack of research on it. In our study, it was observed that the knockout of the SHORTROOT 2 (OsSHR2) which was induced by N deficiency, can significantly affect the regulation of plant architecture response to N in rice. Under N deficiency, the mutation of OsSHR2 significantly reduced root growth, and impaired the sensitivity of the root meristem length to N deficiency. The mutants were found to have approximately a 15% reduction in plant height compared to wild type. But mutants showed a significant increase in tillering at post-heading stage, approximately 26% more than the wild type, particularly in high N conditions. In addition, due to reduced seed setting rate and 1000-grain weight, mutant yield was significantly decreased by approximately 33% under low N fertilizer supply. The mutation also changed the distribution of N between the vegetative and reproductive organs. Our findings suggest that the transcription factor OsSHR2 plays a regulatory role in the response of plant architecture and yield per plant to N in rice.

An ATP-binding cassette transporter, OsABCB24, is involved in female gametophyte development and early seed growth in rice.

Female gametogenesis has been rarely studied due to gametophyte lethality and the unavailability of related genetic resources. In this study, we identified a rice ATP-binding cassette transporter, OsABCB24, whose null function displayed a significantly reduced seed setting rate by as much as 94%-100% compared with that of the wild type (WT). The reciprocal cross of WT and mutant plants demonstrated that the female reproductive organs in mutants were functionally impaired. Confocal microscopy observations revealed that, although megasporogenesis remained unaffected in CRISPR/Cas9 osabcb24 mutants, the formation of female gametophytes was interrupted. Additionally, the structure of the syncytial nucleus was impaired during the initial stages of endosperm formation. Histochemical analysis showed that OsABCB24 was preferentially expressed at the conjunction of receptacle and ovary, spanning from the functional megaspore stage to the two-nucleate embryo sac stage. Further, OsABCB24 was identified as an endoplasmic reticulum membrane-localized protein. Notably, the overexpression of OsABCB24 triggered a 1.5- to 2-fold increase in grain production compared to the WT. Our findings showed that OsABCB24 plays a key role in both female gametophyte development and the early development of seeds.

Functional study of the soybean stamen-preferentially expressed gene GmFLA22a in regulating male fertility.

China has a high dependence on soybean imports, yield increase at a faster rate is an urgent problem that need to be solved at present. The application of heterosis is one of the effective ways to significantly increase crop yield. In recent years, the development of an intelligent male sterility system based on recessive nuclear sterile genes has provided a potential solution for rapidly harnessing the heterosis in soybean. However, research on male sterility genes in soybean has been lagged behind. Based on transcriptome data of soybean floral organs in our research group, a soybean stamen-preferentially expressed gene GmFLA22a was identified. It encodes a fasciclin-like arabinogalactan protein with the FAS1 domain, and subcellular localization studies revealed that it may play roles in the endoplasmic reticulum. Take advantage of the gene editing technology, the Gmfla22a mutant was generated in this study. However, there was a significant reduction in the seed-setting rate in the mutant plants at the reproductive growth stage. The pollen viability and germination rate of Gmfla22a mutant plants showed no apparent abnormalities. Histological staining demonstrated that the release of pollen grains in the mutant plants was delayed and incomplete, which may due to the locule wall thickening in the anther development. This could be the reason of the reduced seed-setting rate in Gmfla22a mutants. In summary, our study has preliminarily revealed that GmFLA22a may be involved in regulating soybean male fertility. It provides crucial genetic materials for further uncovering its molecular function and gene resources and theoretical basis for the utilization of heterosis in soybean.

Comparative assessment of morphological, cytological, and reproductive characteristics of the spontaneous mixoploid ‘MM 2×/4×’ and its diploid counterpart ‘Miss Manilla’ in Bougainvillea (Bougainvillea × buttiana Honlttum & Standl.)

Polyploidization-triggered chromosome multiplication typically leads to improved agronomic and ornamental characteristics in plants. However, mixoploidy may sometimes occur in spontaneous and artificially induced polyploidization events, and the deficiency of basic information about mixoploidy limits its application in breeding. In this study, the ploidy stability of spontaneous mixoploidy Bougainvillea × buttiana ‘Miss Manila’ (‘MM 2×/4×’) was validated through chromosome counting and flow cytometry analysis. Compared with its diploid counterpart ‘MM 2×’, ‘MM 2×/4×’ exhibited significantly larger size in the morphological characters related to leaf, bract, thorn, and perianth tube. The average length, width, and density of stomata in ‘MM 2×/4×’ were also significantly larger than in ‘MM 2×’, while the stomatal density of mesophyll cells decreased. The anthers of ‘MM 2×/4×’produced both 1n and 2n pollen grains, which in vitro germinated reached 8.92 %, significantly higher than ‘MM 2×’ (0.36 %). The seed setting rate of the crossing combinations ‘MM 2×/4×’ × ‘Chitra’, ‘Chitra’ × ‘MM 2×/4×’ and ‘MM 2×/4×’ × ‘Bixi’ were 65.47 %, 32.36 %, and 53.17 %, respectively, and the ploidy levels among different offspring individuals of the same genetic population are relatively consistent. While ‘MM 2×’ could not be hybrid with either the tetraploid ‘Chitra’ or diploid ‘Bixi’. Therefore, the mixoploid ‘MM 2×/4×’ partially restored the fertility of gametes and might be employed for both ploidy breeding directly and creating hybrid segregation populations in bougainvillea for trait genetic dissection.

Response of yield and quality of Japonica rice to different gradients of moisture deficit at grain-filling stage in cold regions

Abstract Water stress significantly affects on rice yield and quality. Eight Japonica varieties from the first and second accumulated temperature zones of Heilongjiang Province were used as materials and four moisture gradients (0, −10, −25 and −40 kPa) were conducted at the grain-filling stage to clarify the effect of water stress on the rice yield and quality in cold regions. The results showed that the rice yield was reduced due to the decrease in the seed setting rate. Rice chalkiness was significantly increased by drought stress, especially under −10 kPa. The protein content of most varieties was significantly reduced and taste quality was increased under −25 to −40 kPa. The effect on protein components increased with increasing drought stress. The gel consistency decreased and the average chain length of amylopectin was less affected by drought. With an increase in moisture deficit, the rapid viscosity analyzer characteristics and chain length distribution of amylopectin showed a trend of first increasing and then decreasing or decreasing and then increasing. The response of starch to mild and severe drought varied. Our study provides a theoretical basis for the efficient utilization of water and high quality and yield of Japonica rice.

OsmiR5519 regulates grain size and weight and down-regulates sucrose synthase gene RSUS2 in rice (Oryza sativa L.).

The up-regulation of OsmiR5519 results in the decrease of grain size, weight and seed setting rate. OsmiR5519 plays important roles in the process of grain filling and down-regulates sucrose synthase gene RSUS2. MicroRNAs (miRNAs) are one class of small non-coding RNAs that act as crucial regulators of plant growth and development. In rice, the conserved miRNAs were revealed to regulate the yield components, but the function of rice-specific miRNAs has been rarely studied. The rice-specific OsmiR5519 was found to be abundantly expressed during reproductive development, but its biological roles remain unknown. In this study, the function of rice-specific OsmiR5519 was characterized with the miR5519-overexpressing line (miR5519-OE) and miR5519-silenced line (STTM5519). At seedling stage, the content of sucrose, glucose and fructose was obviously lower in the leaves of miR5519-OE lines than those of wild-type (WT) line. The grain size and weight were decreased significantly in miR5519-OE lines, compared to those of WT rice. The cell width of hull in miR5519-OE was smaller than that in WT. The seed setting rate was notably reduced in miR5519-OE lines, but not in STTM5519 lines. Cytological observation demonstrated that the inadequate grain filling was the main reason for the decline of seed setting rate in miR5519-OE lines. The percentage of the defects of grain amounted to 40% in miR5519-OE lines, which almost equaled to the decreased value of seed setting rate. Furthermore, the sucrose synthase gene RSUS2 was identified as a target of OsmiR5519 via RNA ligase-mediated 3'-amplification of cDNA ends (3'-RLM-RACE), dual luciferase assays and transient expression assays. In summary, our results suggest that OsmiR5519 regulates grain size and weight and down-regulates RSUS2 in rice.