Increased Tiller Number Research Articles

Functional Analysis of the teosinte branched 1 Gene in the Tetraploid Switchgrass (Panicum virgatum L.) by CRISPR/Cas9-Directed Mutagenesis.

Tillering is an important biomass yield component trait in switchgrass (Panicum virgatum L.). Teosinte branched 1 (tb1)/Branched 1 (BRC1) gene is a known regulator for tillering/branching in several plant species; however, its role on tillering in switchgrass remains unknown. Here, we report physiological and molecular characterization of mutants created by CRISPR/Cas9. We successfully obtained nonchimeric Pvtb1a and Pvtb1b mutants from chimeric T0 mutants using nodal culture. The biallelic Pvtb1a-Pvtb1b mutant plants produced significantly more tillers and higher fresh weight biomass than the wild-type plants. The increased tiller number in the mutant plants resulted primarily from hastened outgrowth of lower axillary buds. Increased tillers were also observed in transgene-free BC1 monoallelic mutants for either Pvtb1a-Pvtb1b or Pvtb1b gene alone, suggesting Pvtb1 genes act in a dosage-dependent manner. Transcriptome analysis showed 831 genes were differentially expressed in the Pvtb1a-Pvtb1b double knockdown mutant. Gene Ontology analysis revealed downregulation of Pvtb1 genes affected multiple biological processes, including transcription, flower development, cell differentiation, and stress/defense responses in edited plants. This study demonstrates that Pvtb1 genes play a pivotal role in tiller production as a negative regulator in switchgrass and provides opportunities for further research aiming to elucidate the molecular pathway regulating tillering in switchgrass.

Morphological and phenological adaptation for convergent development of tillers in Widely spaced wheat sown on different dates

ABSTRACT This study analyzes the dynamics of leaf and tiller emergence and development of widely spaced wheat sown on different dates. We used the phyllochron (time interval between the emergence of successive leaves at the same stage), site filling (the relative rate of increase in the number of tillers per phyllochron), and indices associated with ‘the synchronous growth’. Number of productive tillers per plant (including the main shoot, MS) reached 45.7 in early sowing, and significantly decreased by the delay in sowing. The increase in tiller number with the elapse of leaf age (Haun stage) of MS (HSms) was almost the same as that expected from synchronous growth until HSms 8.6 and site filling before this HSms was close to 0.481. The phyllochron was shortest in MS and increased in axillary tillers with increasing tiller order and position, but the differences in phyllochron between MS and axillary tillers within a plant were significant only at higher order and positions of tillers. The time of emergence of tillers was always advanced in comparison with that expected from synchronous growth. A very close negative linear relationship was found between the number of days from emergence to heading of tillers and the time of their emergence expressed as day of year; this relationship was independent of the tiller order, position and sowing date. Although the phyllochron gradually became longer, a progressive decrease of the leaf and spikelet per spike with the increasing tiller order and position may contribute considerably to the convergence to heading time.

Enhanced OsNLP4-OsNiR cascade confers nitrogen use efficiency by promoting tiller number in rice.

Increased use of nitrogen fertilizers has deleterious impact on the environment. Increase in yield potential at low nitrogen supply is regarded as a cereal breeding goal for future agricultural sustainability. Although natural variations of nitrogen transporters have been investigated, key genes associated with assimilation remain largely unexplored for nitrogen use efficiency (NUE) enhancement. Here, we identified a NIN‐like protein NLP4 associated with NUE through a GWAS in rice. We found that OsNLP4 transactivated OsNiR encoding nitrite reductase that was critical in nitrogen assimilation in rice. We further constructed quadrupling NREs (Nitrate‐responsive cis‐elements) in the promoter of OsNiR (p4xNRE:OsNiR) and enhanced nitrogen assimilation significantly. We demonstrated that OsNLP4‐OsNiR increased tiller number and yield through enhancing nitrogen assimilation and NUE. Our discovery highlights the genetic modulation of OsNLP4‐OsNiR signalling cascade as a strategy for high NUE and yield breeding in rice.

Fungal endophyte diversity in Paspalum and effects on plant growth

AbstractIn natural ecosystems, plants appear to be in symbiosis with diverse fungal endophytes which can have impacts on plant communities. Paspalum is one of the most important grass genera in South American grasslands. The aim of this work was to determine the presence of fungal endophytes in two Paspalum species and evaluate their effects on plant growth. Sixty plant samples were collected for Paspalum notatum in a rangeland in northeastern Argentina, and the same number for Paspalum dilatatum in central Argentina. A triple‐sterilization process was carried out by submerging small pieces of leaves and stems for the isolation of fungi from the collected plants. In order to identify endophytes, morphological characters and fungal sequences corresponding to the ITS (Internal Transcribed Spacer) region were analysed. A total of eight genera were identified: Acremonium, Alternaria, Aspergillus, Bipolaris, Cladosporium, Fusarium, Penicillium and Trichoderma. A greenhouse trial was conducted to determine the effects of fungal endophytes on growth. Trichoderma significantly increased relative chlorophyll content in P. notatum and Acremonium endophytes increased tiller number, and above‐ and below‐ground biomass in P. dilatatum. The diversity of fungal endophytes that was present in P. notatum and P. dilatatum was described. In conclusion, some aspects of growth of these Paspalum species seem to be positively affected by Trichoderma and Acremonium.

Production of novel beneficial alleles of a rice yield-related QTL by CRISPR/Cas9.

Production of novel beneficial alleles of a rice yield-related QTL by CRISPR/Cas9.

Rice siR109944 suppresses plant immunity to sheath blight and impacts multiple agronomic traits by affecting auxin homeostasis.

Plant small RNAs (sRNAs) play significant roles in regulating various developmental processes and hormone signalling pathways involved in plant responses to a wide range of biotic and abiotic stresses. However, the functions of sRNAs in response to rice sheath blight remain unclear. We screened rice (Oryza sativa) sRNA expression patterns against Rhizoctonia solani and found that Tourist-miniature inverted-repeat transposable element (MITE)-derived small interfering RNA (siRNA) (here referred to as siR109944) expression was clearly suppressed upon R.solani infection. One potential target of siR109944 is the F-Box domain and LRR-containing protein 55 (FBL55), which encode the transport inhibitor response 1 (TIR1)-like protein. We found that rice had significantly enhanced susceptibility when siR109944 was overexpressed, while FBL55 OE plants showed resistance to R.solani challenge. Additionally, multiple agronomic traits of rice, including root length and flag leaf inclination, were affected by siR109944 expression. Auxin metabolism-related and signalling pathway-related genes were differentially expressed in the siR109944 OE and FBL55 OE plants. Importantly, pre-treatment with auxin enhanced sheath blight resistance by affecting endogenous auxin homeostasis in rice. Furthermore, transgenic Arabidopsis overexpressing siR109944 exhibited early flowering, increased tiller numbers, and increased susceptibility to R.solani. Our results demonstrate that siR109944 has a conserved function in interfering with plant immunity, growth, and development by affecting auxin homeostasis in planta. Thus, siR109944 provides a genetic target for plant breeding in the future. Furthermore, exogenous application of indole-3-acetic acid (IAA) or auxin analogues might effectively protect field crops against diseases.

Comparative Study of Rice Yield Production for Conventional Paddy Rice and Systems of Rice Intensification

Food security in Kenya is at stake due to decline in farm productivity with a combination of an ever increasing population and worsened by global warming. Improvement of agricultural productivity may not be realized soon as rice farmers currently uses traditional method of flooding rice which has been reported to yield low rice. There is need for a deliberate use of new agricultural technologies that improves productivity of rice farming. System of Rice intensification (SRI) provides an opportunity of yield improvements in rice production. This study was undertaken in Ahero Irrigation Scheme to compare yield production of conventional and SRI rice production for IR 2793-80-1 cultivar. The experiment was laid out in a randomized complete block design with three replications. SRI experiments recorded higher number of effective tillers with experiment having a spacing of 20cm by 20cm and transplanted at 8-11 days gave 321 per m² as compared to 226 effective tillers/m². Seed yield/plant was highly significant in SRI (39.61 g) as compared to a traditional paddy system (17.32 g). Transplanting rice seedling at the age of 8 to 11 days and at 20cm by 20cm spacing recorded highest seed yield/ha of 4.7 t/ha as compared to traditional flooding which recorded 2.7 t/ha. These results imply that planting young rice seedlings improves grain yield because of increase in number of tillers per square meters, plant height and better plant rooting ability.

Clipping defoliation and nitrogen addition shift competition between a C3 grass (Leymus chinensis) and a C4 grass (Hemarthria altissima).

Human-induced disturbances, including grazing and clipping, that cause defoliation are common in natural grasslands. Plant functional type differences in the ability to compensate for this tissue loss may influence interspecific competition. To explore the effects of different intensities of clipping and nitrogen (N) addition on compensatory growth and interspecific competition, we measured accumulated aboveground biomass (AGB), belowground biomass (BGB), tiller number, non-structural carbohydrates concentrations and leaf gas exchange parameters in two locally co-occurring species (the C3 grass Leymus chinensis and the C4 grass Hemarthria altissima) growing in monoculture and in mixture. For both grasses, the clipping treatment had significant impacts on the accumulated AGB, and the 40% clipping treatment had the largest effect. BGB gradually decreased with increasing defoliation intensity. Severe defoliation caused a significant increase in tiller number. Stored carbohydrates in the belowground biomass were mobilised and transported aboveground for the growth of new leaves to compensate for clipping-induced injury. The net CO2 assimilation rate (A) of the remaining leaves increased with clipping intensity and peaked under clipping intensities of 20% or 40%. Nitrogen addition, at a rate of 10g·N·m-2 ·year-1 , enhanced A of the remaining leaves and non-structural carbohydrate concentrations, which benefited plant compensatory growth, especially for the C3 grass. Under the mixed planting conditions, the clipping and N addition treatments lowered the competitive advantage of the C4 grass. The results suggest that a combination of defoliation and N deposition have the potential to benefit the coexistence of C3 and C4 grasses.

Differences in the photosynthetic and physiological responses of Leymus chinensis to different levels of grazing intensity

BackgroundGrazing is an important land use in northern China. In general, different grazing intensities had a different impact on the morphological and physiological traits of plants, and especially their photosynthetic capacity. We investigated the responses of Leymus chinensis to light, medium, and heavy grazing intensities in comparison with a grazing exclusion control.ResultsWith light grazing, L. chinensis showed decreased photosynthetic capacity. The low chlorophyll and carotenoid contents constrained light energy transformation and dissipation, and Rubisco activity was also low, restricting the carboxylation efficiency. In addition, the damaged photosynthetic apparatus accumulated reactive oxygen species (ROS). With medium grazing, more energy was used for thermal dissipation, with high carotene content and high non-photochemical quenching, whereas photosynthetic electron transport was lowest. Significantly decreased photosynthesis decreased leaf C contents. Plants decreased the risk caused by ROS through increased energy dissipation. With high grazing intensity, plants changed their strategy to improve survival through photosynthetic compensation. More energy was allocated to photosynthetic electron transport. Though heavy grazing damaged the chloroplast ultrastructure, adjustment of internal mechanisms increased compensatory photosynthesis, and an increased tiller number facilitated regrowth after grazing.ConclusionsOverall, the plants adopted different strategies by adjusting their metabolism and growth in response to their changing environment.

Tillering and small grain 1 dominates the tryptophan aminotransferase family required for local auxin biosynthesis in rice.

Auxin is a crucial phytohormone, controlling multiple aspects of plant growth and responses to the changing environment. However, the role of local auxin biosynthesis in specific developmental programs remains unknown in crops. This study characterized the rice tillering and small grain 1 (tsg1) mutant, which has more tillers but a smaller panicle and grain size resulting from a reduction in endogenous auxin. TSG1 encodes a tryptophan aminotransferase that is allelic to the FISH BONE (FIB) gene. The tsg1 mutant showed hypersensitivity to indole-3-acetic acid and the competitive inhibitor of aminotransferase, L-kynurenine. TSG1 knockout resulted in an increased tiller number but reduction in grain number and size, and decrease in height. Meanwhile, deletion of the TSG1 homologs OsTAR1, OsTARL1, and OsTARL2 caused no obvious changes, although the phenotype of the TSG1/OsTAR1 double mutant was intensified and infertile, suggesting gene redundancy in the rice tryptophan aminotransferase family. Interestingly, TSG1 and OsTAR1, but not OsTARL1 and OsTARL2, displayed marked aminotransferase activity. Meanwhile, subcellular localization was identified as the endoplasmic reticulum, while phylogenetic analysis revealed functional divergence of TSG1 and OsTAR1 from OsTARL1 and OsTARL2. These findings suggest that TSG1 dominates the tryptophan aminotransferase family, playing a prominent role in local auxin biosynthesis in rice.

Cyclic 3-hydroxymelatonin exhibits diurnal rhythm and cyclic 3-hydroxymelatonin overproduction increases secondary tillers in rice by upregulating MOC1 expression

Cyclic 3-hydroxymelatonin (c3OHM) is a major metabolite of melatonin in plants produced by the enzymatic action of melatonin 3-hydroxylase (M3H). However, the function of c3OHM in plants is unclear. Here, we report that M3H mRNA and c3OHM levels display diurnal rhythms with peaks at night, but not in a circadian manner. This diurnal rhythmicity occurred predominantly in the late vegetative growth stage (8 weeks after germination), but was absent in the early vegetative growth stage. Transgenic rice plants overexpressing or underexpressing M3H were generated to investigate the physiological roles of diurnal production of c3OHM. The M3H-overexpression (OE) line exhibited higher M3H activity and c3OHM production than the wild-type, and vice versa for the M3H‑underexpression rice (RNAi). The seedling growth phenotype of the OE and RNAi lines was comparable to that of the wild-type but exhibited pleiotropic phenotypic defects at the reproductive stage, such as decreased height, biomass, grain yield, and fertility. Of note, the OE rice showed significantly increased numbers of secondary tillers and panicles. The increase in tiller number of the OE line was linked to increased expression of tiller-related genes, such as MOC1 and TB1, suggesting that the diurnal rhythm of c3OHM production is associated with the tiller number, a pivotal agronomic trait governing grain yield in rice.

Comparative FISH and molecular identification of new stripe rust resistant wheat-Thinopyrum intermedium ssp. trichophorum introgression lines

Thinopyrum intermedium (2n = 6x = 42, JJJsJsStSt) has been hybridized extensively with common wheat and has proven to be a valuable germplasm source for improving disease resistance, quality attributes, and yield potential in wheat. We characterized new disease resistant wheat-Th. intermedium derivatives A1082 and A5-5 using sequential multi-color fluorescence in situ hybridization (mc-FISH), genomic in situ hybridization (GISH), PCR-based landmark unique gene (PLUG) and intron targeting (IT) markers. A1082 was identified as a wheat-Th. intermedium 3J disomic addition line, and A5-5 was a T4BS·5JsL homozygous Robertsonian translocation line. Seventy-one and 106 pairs of primers amplified Th. intermedium-specific bands allowing chromosomes 3J and 5Js to be tracked, respectively. A new oligonucleotide probe, Oligo-6H-2-100, was developed for FISH labeling of the subterminal region of the long arm of chromosome 5Js. Both lines were highly resistant to stripe rust pathogen races prevalent in Chinese field screening nurseries. A5-5 also displayed a significant increase in tiller number compared to its wheat parent. The new lines can be exploited as useful germplasms for wheat improvement.

SLR1 inhibits MOC1 degradation to coordinate tiller number and plant height in rice

The breeding of cereals with altered gibberellin (GA) signaling propelled the ‘Green Revolution’ by generating semidwarf plants with increased tiller number. The mechanism by which GAs promote shoot height has been studied extensively, but it is not known what causes the inverse relationship between plant height and tiller number. Here we show that rice tiller number regulator MONOCULM 1 (MOC1) is protected from degradation by binding to the DELLA protein SLENDER RICE 1 (SLR1). GAs trigger the degradation of SLR1, leading to stem elongation and also to the degradation of MOC1, and hence a decrease in tiller number. This discovery provides a molecular explanation for the coordinated control of plant height and tiller number in rice by GAs, SLR1 and MOC1.

OsSHI1 Regulates Plant Architecture Through Modulating the Transcriptional Activity of IPA1 in Rice.

Tillering and panicle branching are important determinants of plant architecture and yield potential in rice (Oryza sativa). IDEAL PLANT ARCHITECTURE1 (IPA1) encodesSQUAMOSA PROMOTER BINDING PROTEIN-LIKE14, which acts as a key transcription factor regulating tiller outgrowth and panicle branching by directly activating the expression of O. sativa TEOSINTE BRANCHED1 (OsTB1) and O. sativa DENSE AND ERECT PANICLE1 (OsDEP1), thereby influencing grain yield in rice. Here, we report the identification of a rice mutant named shi1 that is characterized by dramatically reduced tiller number, enhanced culm strength, and increased panicle branch number. Map-based cloning revealed that O. sativa SHORT INTERNODES1 (OsSHI1) encodes a plant-specific transcription factor of the SHI family with a characteristic family-specific IGGH domain and a conserved zinc-finger DNA binding domain. Consistent with the mutant phenotype, OsSHI1 is predominantly expressed in axillary buds and young panicle, and its encoded protein is exclusively targeted to the nucleus. We show that OsSHI1 physically interacts with IPA1 both in vitro and in vivo. Moreover, OsSHI1 could bind directly to the promoter regions of both OsTB1 and OsDEP1 through a previously unrecognized cis-element (T/GCTCTAC motif). OsSHI1 repressed the transcriptional activation activity of IPA1 by affecting its DNA binding activity toward the promoters of both OsTB1 and OsDEP1, resulting in increased tiller number and diminished panicle size. Taken together, our results demonstrate that OsSHI1 regulates plant architecture through modulating the transcriptional activity of IPA1 and provide insight into the establishment of plant architecture in rice.

Complex epigenetic regulation of alkaloid biosynthesis and host interaction by heterochromatin protein I in a fungal endophyte-plant symbiosis

Epichloë festucae forms mutualistic symbiotic interactions with grasses of the Lolium and Festuca genera. Protection from insect and mammalian herbivory are the best-documented host benefits of these associations. The two main classes of anti-mammalian alkaloids synthesized by E. festucae are the ergot alkaloids and indole diterpenes, of which ergovaline and lolitrems are the principal terminal products. Synthesis of both metabolites require multiple gene products encoded by clusters of 11 genes located at the subtelomeric regions of chromosomes I and III respectively. These loci are essentially unexpressed in axenic culture but among the most highly expressed genes in planta. We show here that heterochromatin 1 protein (HepA) is an important component of the regulatory machinery that maintains these loci in a silent state in culture. Deletion of this gene led to derepression of eas and ltm gene expression under non-symbiotic culture conditions. Although there was no obvious culture phenotype, RNAseq analysis revealed that around 1000 genes were differentially expressed in the ΔhepA mutant compared to wild type with just one-third upregulated. Inoculation of the ΔhepA mutants into seedlings of Lolium perenne led to a severe host interaction phenotype characterized by a reduction in tiller length but an increase in tiller number. Hyphae within the leaves of these associations were much more abundant in the intercellular spaces of the leaves and aberrantly colonized the vascular bundles. This physiological change was accompanied by a dramatic change in the transcriptome with around 900 genes differentially expressed, with two thirds of these upregulated. This major physiological change was accompanied by a decrease in ltm gene expression and loss of the ability to synthesize lolitrems. These results show that HepA has an important role in controlling the chromatin state of these sub-telomeric secondary metabolite genes, including their symbiosis-specific regulation.

OsSPL18 controls grain weight and grain number in rice

Grain weight and grain number are two important traits directly determining grain yield in rice. To date, a lot of genes related to grain weight and grain number have been identified; however, the regulatory mechanism underlying these genes remains largely unknown. In this study, we studied the biological function of OsSPL18 during grain and panicle development in rice. Knockout (KO) mutants of OsSPL18 exhibited reduced grain width and thickness, panicle length and grain number, but increased tiller number. Cytological analysis showed that OsSPL18 regulates the development of spikelet hulls by affecting cell proliferation. qRT-PCR and GUS staining analyses showed that OsSPL18 was highly expressed in developing young panicles and young spikelet hulls, in agreement with its function in regulating grain and panicle development. Transcriptional activation experiments indicated that OsSPL18 is a functional transcription factor with activation domains in both the N-terminus and C-terminus, and both activation domains are indispensable for its biological functions. Quantitative expression analysis showed that DEP1, a major grain number regulator, was significantly down-regulated in OsSPL18 KO lines. Both yeast one-hybrid and dual-luciferase (LUC) assays showed that OsSPL18 could bind to the DEP1 promoter, suggesting that OsSPL18 regulates panicle development by positively regulating the expression of DEP1. Sequence analysis showed that OsSPL18 contains the OsmiR156k complementary sequence in the third exon; 5ʹ RLM-RACE experiments indicated that OsSPL18 could be cleaved by OsmiR156k. Taken together, our results uncovered a new OsmiR156k-OsSPL18-DEP1 pathway regulating grain number in rice.

Transgenic Rice Overexperessing a Tomato Mitochondrial Phosphate Transporter, SlMPT3;1, Promotes Phosphate Uptake and Increases Grain Yield

Mitochondrial phosphate transporter plays an important regulatory role in promoting the uptake and transport of phosphate in plants. In this study, the SlMPT3;1 gene, a member of mitochondrial phosphate transporter family in tomato, was isolated and transformed into the rice Oryza sativa L. ssp. japonica cultivar Kitaake. The SlMPT3;1 is localized to the mitochondrial membrane and functions in compensating the phosphate uptake in yeast MB192 mutant that is defective in phosphate transport under Pi deficiency. RT-qPCR showed that the SlMPT3;1 is expressed in all of tomato tissues, but highly accumulated in the young leaves and stems under Pi deficiency. The data demonstrated that at least two copies of the SlMPT3;1 gene are inserted into the rice genome, and the transcripts of the SlMPT3;1 mRNA are highly accumulated in the roots of the transgenic rice. The overexpression of the SlMPT3;1 gene not only promotes phosphate uptake by the roots, but also increases the translocation of phosphate from the roots to the shoots in the transgenic rice. The transgenic rice accumulated more chlorophyll and soluble sugar in the shoots than the wild type under Pi deficiency. Microassay sequencing showed that the differentially expressed genes in the transgenic rice are mainly involved in the regulations of biological process and molecular function under Pi deficiency. Further RTqPCR analyses revealed that the differentially expressed genes, which are involved in the regulations of the biological process, cell component, and molecular function, are upregulated under Pi deficiency, and exhibit similar expression trends to the relative expression folds of these partial differentially expressed genes in the transcriptomic analyses. This study suggests that the overexpression of the SlMPT3;1 gene promoted the uptake and transport of phosphate in rice, thus leading to an enhanced increase in tiller number and effective panicle of per plant, and increasing grain yield under Pi deficiency.

An investigation of genotype-phenotype association in a festulolium forage grass population containing genome-spanning Festuca pratensis chromosome segments in a Lolium perenne background.

Alien chromosome introgression is used for the transfer of beneficial traits in plant breeding. For temperate forage grasses, much of the work in this context has focused on species within the ryegrasses (Lolium spp.) and the closely related fescues (Festuca spp.) particularly with a view to combining high forage quality with reliability and enhanced environmental services. We have analysed a L. perenne (perennial ryegrass) population containing the majority of a F. pratensis (meadow fescue) genome as introgressed chromosome segments to identify a) marker-trait associations for nutrient use and abiotic stress response across the family, and b) to assess the effects of introgression of F. pratensis genomic regions on phenotype. Using container-based assays and a system of flowing solution culture, we looked at phenotype responses, including root growth, to nitrogen and phosphorus status in the growing medium and abiotic stresses within this festulolium family. A number of significant marker/trait associations were identified across the family for root biomass on chromosomes 2, 3 and 5 and for heading date on chromosome 2. Of particular interest was a region on chromosome 2 associated with increased root biomass in phosphorus-limited conditions derived from one of the L. perenne parents. A genotype containing F. pratensis chromosome 4 as a monosomic introgression showed increased tiller number, shoot and root growth and genotypes with F. pratensis chromosome segment introgressions at different ends of chromosome 4 exhibited differential phenotypes across a variety of test conditions. There was also a general negative correlation between the extent of the F. pratensis genome that had been introgressed and root-related trait performances. We conclude that 1) the identification of alleles affecting root growth has potential application in forage grass breeding and, 2) F. pratensis introgressions can enhance quantitative traits, however, introgression can also have more general negative effects.

Nitrogen application after low-temperature exposure alleviates tiller decrease in rice

Low temperature during the vegetative stage depresses the rice tillering, which decreases rice yield. The production and development of rice tillers can be closely related to the presence of nitrogen. Therefore, supplying rice with nitrogen after exposure to low temperatures may be an effective method to promote rice tillering. However, there is limited research about the effects of nitrogen application after low-temperature exposure on rice tillering. Water culture and field experiments were conducted using two rice varieties in each experiment; three temperatures (12 °C, 15 °C and 18 °C) and temperature durations (5, 10 and 15 days under 15 °C) were set in water culture experiments, and two temperatures (approximately 13 °C and 17 °C) were set in the field experiment. Two (40 mg N L−1 and 80 mg N L−1) and four (0, 20, 40 and 80 kg N ha−1) nitrogen levels after temperature treatment were applied in the water culture and field experiments, respectively. The results showed that low temperatures decreased rice tillering, nitrogen accumulation and yield, and higher stress strengths or longer low temperature durations led to greater tiller suppression. Nitrogen application after low-temperature stress enhanced the recovery of rice tillering. Four weeks after nitrogen application, the rice tiller number recovered to 87.90–92.92% of normal levels under 15 °C and to 70.39–73.85% of normal levels under 12 °C. Tillering in sensitive rice could be recovered to levels found at normal temperatures at the 10.5-leaf stage with increased nitrogen application after 5 days at 15 °C, whereas insensitive rice could be recovered without increased nitrogen. When low-temperature stress lasted for more than 10 days, increasing nitrogen application improved rice growth as well, although neither variety’s tillering recovered to normal levels. The correlation analysis also showed that the increase in tiller number was closely related to the increase in nitrogen accumulation (P < 0.01). Moreover, increasing the nitrogen application after low temperatures increased the rice nitrate reductase (NR) and glutamine synthase (GS) activities and nitrogen accumulation. The field experiment also showed that increasing the nitrogen application after low temperature could help rice yield recovery, but applying excessive nitrogen (more than 40 kg N ha-1 in this experiment) resulted in yield and nitrogen loss. These results highlighted the positive effects of nitrogen on rice growth recovery after low-temperature stress, which was affected by low temperature strength, duration and rice variety.

Rice SDSFL1 plays a critical role in the regulation of plant structure through the control of different phytohormones and altered cell structure

Semi-dwarfism is one of the most important agronomic traits for many cereal crops. In the present study, a mutant with semi-dwarf and short flag leaf 1, sdsfl1, was identified and characterized. The sdsfl1 mutant demonstrated some distinguished structural alterations, including shorter plant height and flag leaf length, increased tiller numbers and flag leaf width, and decreased panicle length compared with those of wild type (WT). Genetic analysis suggested that the mutant traits were completely controlled by a single recessive gene. The SDSFL1 gene was mapped to the long arm of chromosome 3 within a region of 44.6 kb between InDel markers A3P8.3 and A3P8.4. The DNA sequence analysis revealed that there was only a T to C substitution in the coding region of LOC_Os03g63970, resulting in the substitution of Tryptophan (Try) to Arginine (Arg) and encoding a GA 20 oxidase 1 protein of 372 amino acid residues. Photosynthesis analysis showed that the photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular CO2 concentration (Ci) were significantly increased in sdsfl1. Chlorophyll a (Chl a), total Chl, and carotenoid contents were significantly increased in sdsfl1 compared with those in WT. sdsfl1 carried a reduced level of GA3 but reacted to exogenously applied gibberellins (GA). Moreover, the levels of abscisic acid (ABA), indole 3-acetic acid (IAA), and salicylic acid (SA) were notably improved in sdsfl1, whereas there was no noteworthy change in jasmonic acid (JA). The results thus offer a visible foundation for the molecular and physiological analysis of the SDSFL1 gene, which might participate in various functional pathways for controlling plant height and leaf length in rice breeding.