Spikelet Development Research Articles

Loss of function of OsMADS34 leads to large sterile lemma and low grain yield in rice (Oryza sativa L.)

Rice (Oryza sativa L.) is one of the most important food crops, especially in Asia. The spikelet is a characteristic structure of grass inflorescences that determines crop output. However, the molecular mechanism that controls spikelet development and grain yield in rice remains unclear. In this study, we isolated a new osmads34 allelic mutant (i.e., osmads34-t). The osmads34-t mutant showed more primary branch numbers, short panicles, and long sterile lemmas. The sterile lemmas were transformed into the lemmas and had the lemma identity in the osmads34-t mutant, suggesting that the sterile lemma and lemma are homologous organs. Additionally, osmads34-t displayed smaller grains on its secondary branches of panicles and a lower seed-setting rate. These results suggest that OsMADS34 plays an important role in determination of grain size and yield in rice. OsMADS34 was expressed in tested organs and tissues, and its green fluorescent protein (GFP) signal was located in the nucleus. The result of this study will be used to understand the identity of unique organs in grass spikelets and may improve grain yield in breeding practice.

Dynamic changes of small RNAs in rice spikelet development reveal specialized reproductive phasiRNA pathways

Dissection of the genetic pathways and mechanisms by which anther development occurs in grasses is crucial for both a basic understanding of plant development and for examining traits of agronomic importance such as male sterility. In rice, MULTIPLE SPOROCYTES1 (MSP1), a leucine-rich-repeat receptor kinase, plays an important role in anther development by limiting the number of sporocytes. OsTDL1a (a TPD1-like gene in rice) encodes a small protein that acts as a cofactor of MSP1 in the same regulatory pathway. In this study, we analyzed small RNA and mRNA changes in different stages of spikelets from wild-type rice, and from msp1 and ostdl1a mutants. Analysis of the small RNA data identified miRNAs demonstrating differential abundances. miR2275 was depleted in the two rice mutants; this miRNA is specifically enriched in anthers and functions to trigger the production of 24-nt phased secondary siRNAs (phasiRNAs) from PHAS loci. We observed that the 24-nt phasiRNAs as well as their precursor PHAS mRNAs were also depleted in the two mutants. An analysis of co-expression identified three Argonaute-encoding genes (OsAGO1d, OsAGO2b, and OsAGO18) that accumulate transcripts coordinately with phasiRNAs, suggesting a functional relationship. By mRNA in situ analysis, we demonstrated a strong correlation between the spatiotemporal pattern of these OsAGO transcripts and phasiRNA accumulations.

Morphogenesis and Gene Mapping of deformed interior floral organ 1 (difo1), a Novel Mutant Associated with Floral Organ Development in Rice

Floral organ identity and specific number directly affect anthesis habits, fertilization and grain yield. Here, we identified a deformed interior floral organ 1 (difo1) mutant from selfing progenies of indica cv. Zhonghui8015 (Zh8015) after 60Co γ-ray treatment. Compared with the Zh8015 spikelet, the interior floral organs of the difo1 mutant present various numbers of stamens and stigmas, with no typical filament and no mature pollen grains. Most difo1 flowers exhibited an increased number of stigmas that were attached to the stamens and an intumescent ovule-like cell mass in addition to the ovary. Transverse sections of spikelets and scanning electron microscopy analysis revealed an indeterminate number of interior floral organs and abnormal early spikelet development for the difo1 mutant. Instead of the linear-shaped surface of wild-type stamens, difo1 displayed a glossy stamen surface resulting in immature stamens and complete sterility. In addition, the difo1 mutant exhibited delayed anthesis, rapid anthesis and non-extended stamens compared with wild type. Genetic analysis and gene mapping revealed that difo1 was controlled by a single recessive gene, which was fine-mapped to a 54-kb interval on the short arm of chromosome 4 between markers S22 and RM16439 harboring nine ORFs. Sequence analysis revealed that the mutant carried a single nucleotide deletion in its promoter region, which likely corresponded to the phenotype, in a C2H2-type zinc finger protein gene (LOC_Os04g08600). Moreover, qRT-PCR analysis showed a significantly down-regulated expression pattern for DIFO1 and many floral organ identity genes in the interior floral organs of difo1. DIFO1 is therefore an important floral organ development gene in rice, particularly with regard to interior organ meristem identity and floret primordium differentiation.

Growth characteristics and endosperm structure of superior and inferior spikelets of indica rice under high-temperature stress

Heat stress severely reduces rice yield and quality; however, differences between the superior, early-flowering and inferior, later-flowering spikelets of indica rice in response to high-temperature stress during grain filling remain unclear. This study investigated the effects of high temperature (HT, 33.6/20.7 °C day/night) on growth, endosperm structure, and hormone and polyamine content of superior and inferior spikelets of heat-sensitive (SG-1) and heat-tolerant (HHZ) indica cultivars. The HT decreased fertilization rate, caused earlier grain filling, and reduced duration of grain filling, thus resulting in decreased grain mass and a poor endosperm structure. In addition, soluble sugar and sucrose content increased, and starch synthesis decreased by HT at the early stage of grain filling. The HT increased polyamine [spermidine (Spd) and spermine (Spm)] and abscisic acid (ABA) content, but reduced zeatin (Z) + zeatin riboside (ZR) and indole-3-acetic acid (IAA) content in the grains. Such effects were more apparent in the inferior than superior spikelets; however, the inferior spikelets of SG-1 were more affected than those of HHZ. At the middle grain filling stage, HT produced little difference between the two cultivars. Our results suggest that the poor development of inferior spikelets of SG-1 under the HT could be attributed, at least in part, to the changed content and ratios of free polyamines [putrescine (Put), Spd, and Spm] and phytohormones (Z+ZR, IAA, and ABA) and the conversion efficiency of sucrose into starch.

Mapping and candidate gene analysis for a new top spikelet abortion mutant in rice

AbstractGrain numbers is one of the determinations for rice yield and directly associated with spikelet numbers per panicle and its normal development. Lots of genes responsible for spikelet numbers and spikelet early development have been identified, but the molecular information about the spikelet development at later development is still limited. Here, we isolated a rice spikelet abnormal development mutant, which shows degenerated spikelet at the top panicle and named aborted top spikelet mutant 1(Ats1). The spikelets derived from the middle and bottom branches per panicle of Ats1 show normal development with those of wild type. However, a large number of branches and spikelets with arrested development were often observed only on apex panicle. The abnormality did not appear until the stage In8 when rachises elongate rapidly and reproductive organs get mature, based on observations through SEM analysis. The aborted spikelet could develop the complete floral organs with a pair of rudimentary glume, a pair of empty glume, two lodicule, six stamens and one carpel. But all these floral organs did not develop maturity. Genetic analysis on two F2 populations indicated that the Ats1 was controlled by a single dominant gene. By using bulked segregant analysis of F2 population developed from Ats1 crossing with Songjing6, ATS1 was mapped on chromosome 8 between RM3819 and RM5556. Then, the fine mapping was performed with 1078 F2 population developed from Ats1 and IR36. The ATS1 locus was finely mapped in an 85.7 kb region between RM22448 and STS8‐2 with 8 genes according to the rice annotation project database. Sequence analysis of the candidate genes within the delimited region of the Ats1 and Akihikari showed two‐nucleotide changes, including single‐nucleotide substitutions corresponding to an amino acid substitution from asparagine to lysine acid in exons 3 and a 1‐bp deletion resulting in a premature stop codon in exon 22 at the candidate gene, LOC_Os08g06480. A cleaved amplified polymorphic sequence (CAPS) marker, CAPS‐ats1, was developed from the 1‐bp deletion site. The complete cosegregation of the CAPS genotypes with the matching phenotypes were observed in the F2 populations. This suggested that Os08g06480 is most likely the ATS1 gene. These results will provide more information for better understanding of the molecular mechanism governing top spikelet abortion within a short developmental period.

Using RNA-seq to Profile Gene Expression of Spikelet Development in Response to Temperature and Nitrogen during Meiosis in Rice (Oryza sativa L.).

Rice reproductive development is sensitive to high temperature and soil nitrogen supply, both of which are predicted to be increased threats to rice crop yield. Rice spikelet development is a critical process that determines yield, yet little is known about the transcriptional regulation of rice spikelet development in response to the combination of heat stress and low nitrogen availability. Here, we profiled gene expression of rice spikelet development during meiosis under heat stress and different nitrogen levels using RNA-seq. We subjected plants to four treatments: 1) NN: normal nitrogen level (165 kg ha-1) with normal temperature (30°C); 2) HH: high nitrogen level (264 kg ha-1) with high temperature (37°C); 3) NH: normal nitrogen level and high temperature; and 4) HN: high nitrogen level and normal temperature. The de novo transcriptome assembly resulted in 52,250,482 clean reads aligned with 76,103 unigenes, which were then used to compare differentially expressed genes (DEGs) in the different treatments. Comparing gene expression in samples with the same nitrogen levels but different temperatures, we identified 70 temperature-responsive DEGs in normal nitrogen levels (NN vs NH) and 135 DEGs in high nitrogen levels (HN vs HH), with 27 overlapping DEGs. We identified 17 and seven nitrogen-responsive DEGs by comparing changes in nitrogen levels in lower temperature (NN vs HN) and higher temperature (NH vs HH), with one common DEG. The temperature-responsive genes were principally associated with cytochrome, heat shock protein, peroxidase, and ubiquitin, while the nitrogen-responsive genes were mainly involved in glutamine synthetase, amino acid transporter, pollen development, and plant hormone. Rice spikelet fertility was significantly reduced under high temperature, but less reduced under high-nitrogen treatment. In the high temperature treatments, we observed downregulation of genes involved in spikelet development, such as pollen tube growth, pollen maturation, especially sporopollenin biosynthetic process, and pollen exine formation. Moreover, we observed higher expression levels of the co-expressed DEGs in HN vs HH compared to NN vs NH. These included the six downregulated genes (one pollen maturation and five pollen exine formation genes), as well as the four upregulated DEGs in response to heat. This suggests that high-nitrogen treatment may enhance the gene expression levels to mitigate aspects of heat-stress. The spikelet genes identified in this study may play important roles in response to the combined effects of high temperature and high nitrogen, and may serve as candidates for crop improvement.

Blocking miR396 increases rice yield by shaping inflorescence architecture.

Strategies to increase rice productivity to meet the global demand have been the main concern of breeders around the world. Although a growing number of functional genes related to crop yield have been characterized, our understanding of its associated regulatory pathways is limited. Using rice as a model, we find that blocking miR396 greatly increases grain yield by modulating development of auxiliary branches and spikelets through direct induction of the growth regulating factor 6 (OsGRF6) gene. The upregulation of OsGRF6 results in the coordinated activation of several immediate downstream biological clades, including auxin (IAA) biosynthesis, auxin response factors, and branch and spikelet development-related transcription factors. This study describes a conserved microRNA (miRNA)-dependent regulatory module that integrates inflorescence development, auxin biosynthesis and signalling pathways, and could potentially be used in engineering high-yield crop plants.

Development of new SSR markers for homoeologous WFZP loci based on the study of structure and location of microsatellites in gene-rich regions of chromosomes 2AS , 2BS, 2DS

Microsatellites, or simple sequence repeats (SSRs), are ubiquitous in genomes of eukaryotes, including plant genomes. The structure and location of SSR loci determine their potential as molecular genetic markers and may have impact on the potential function of microsatellites in important biological processes. Identification and study of the distribution of SSR loci in gene-rich regions of the bread wheat genome and development of novel SSR markers based on these data are of practical interest, being important for the study of bread wheat genome organization. Bread wheat BACclone sequences containing homoeologous WFZP genes that control spikelet development served as the base for the identification and localization of SSR loci in generich regions of chromosomes 2AS, 2BS, and 2DS. It was found that di- and trinucleotide motifs were predominant. The most common dinucleotide motifs were AG and GA/TC. They were distributed in noncoding regions of genes, transposable elements (TEs) and unannotated sequences. Most identified trinucleotide motifs were associated with transposable elements. Homoeologous SSR loci were found in either genes or unannotated sequences. Comparison of these loci showed that the divergence in their structure was caused both by changes in repeat number and nucleotide substitutions. New SSR markers were developed and mapped. On the genetic maps of chromosomes 2A, 2B и 2D, they collocated with the WFZP-A-B-D genes. Thus, they can be used for gene tagging in molecular research and in marker-assisted selection.

Revision of the genus Costularia (Cyperaceae: Schoeneae) for the flora of the Seychelles, including the rediscovery and resurrection of a rare endemic species

Knowledge of the monocot flora of the Seychelles remains relatively weak and new taxonomic studies, including both herbarium specimens and field observations, are needed. Extensive new explorations in the key biodiversity areas of the Seychelles granitic islands resulted in the discovery of an unknown species of Costularia. After careful examination of existing specimens and literature within that genus, we concluded that the unknown plant corresponds to the type of Cladium xipholepis, a species endemic to the Seychelles which had previously been confused and put into synonymy with two unrelated taxa, i.e. the other Seychelles endemic Costularia hornei and the Mascarene species C. melicoides. These confusions were due to the immature state of the type of Cladium xipholepis, which was the only known specimen of the species. The name Cladium xipholepis is here resurrected and combined in the genus Costularia, adding one endemic species to the flora of the Seychelles. In addition, a detailed description is provided, correcting important errors regarding diagnostic characters made in the original description. Costularia xipholepis is a rare species, occurring on lower montane inselbergs of Mahé Island, and is here proposed as endangered (EN) according to IUCN Red List categories and criteria. It is morphologically closely related to C. pantopoda var. baronii from Madagascar. The other Seychelles endemic Costularia, C. hornei (lectotype designated here), has no close relative and belongs to a group distributed in South-East Asia. We discuss these results in relation to the origins of the flora of the Seychelles. Finally, the previously thought endemic variety Costularia hornei var. rectirhachilloidea was also reviewed and we consider it to be identical to the type variety, but based on specimens at an earlier stage of spikelet development. These discoveries, along with other preliminary studies, indicate that more studies are needed to review the monocots of the Seychelles, particularly Cyperaceae, Orchidaceae and Poaceae.

Fine mapping of a palea defective 1 (pd1), a locus associated with palea and stamen development in rice.

KEY MESSAGE : pd1, a genetic factor in a 69 kb region between RM11239 and RM11245 on rice chromosome 1, controls stamen number and palea development. Spikelets are important organs that store photosynthetic products in rice. Spikelet development directly affects grain yield and rice quality. Here, we report a palea defective (pd1) mutant identified from selfing progenies of indica cv. 93-11 after (60)Co γ ray treatment. pd1 mutant flowers only had four stamens (wild-type has six), but pollen fertility was not affected. Compared with 93-11 palea, pd1 mutant palea showed smaller and flatter leaf, which caused the lemma to bend excessively inward. pd1 mutants had only 46% seed setting rate and 21.6 g 1000-grain weight, which led to two-thirds loss of grain yield. Scanning electron microscope analysis revealed that pd1 mutants had reduced epidermal cell size and reduced numbers of fibrous sclerenchyma cells in both palea and lemma. To analyze the genetic factors involved, we crossed pd1 mutants with three japonica cultivars and generated F1 and F2 populations. The F1 phenotype and F2 segregation ratio indicated that a recessive gene controlled the mutant traits. Using the F2 population, we found that pd1 mapped between the simple sequence repeat markers RM11236 and RM11280 on rice chromosome 1. From a segregating population of 2836 plants, 77 recombinants were screened by RM11236 and RM11280. High-resolution linkage analysis narrowed the pd1 locus to a 69 kb region between RM11239 and RM11245 that contained 10 open reading frames (ORFs). Sequence alignment and quantitative real-time PCR expression analysis of these ORFs between 93-11 and pd1 mutant plants found no unequivocal evidence to identify the pd1 gene.

The Rice Floral Repressor Early flowering1 Affects Spikelet Fertility By Modulating Gibberellin Signaling.

BackgroundGibberellic acid (GA; or gibberellin) affects the development of floral organs, especially anthers and pollen, and perturbation of development of male floral organs can cause sterility. Many studies of GA signaling have concentrated on anther development, but the effect of GA on grain production remains to be examined.ResultsUsing a cross of ‘Milyang23 (M23)’, which has a functional allele of Early flowering1 (EL1), and ‘H143’, which has a nonfunctional el1 allele, we generated heterogeneous inbred family-near isogenic lines (HNILs) that are homozygous for EL1 [HNIL(M23)] or el1 [HNIL(H143)]. Here, we found that HNIL(H143) exhibited anther deformities and low pollen viability. The expression of GAMYB, a major activator of GA signaling, and its downstream genes CYP703A3 and KAR, mainly involved in pollen formation, increased abnormally during spikelet development; this activation of GA signaling may cause the sterility. To confirm the negative effect of the el1 mutation on spikelet fertility, we examined a line carrying a T-DNA insertion el1 mutant [hereafter ZH11(el1)] and its parental cultivar ‘Zhonghua11 (ZH11)’. ZH11(el1) showed nearly identical defects in anther development and pollen viability as HNIL(H143), leading to decreased seed setting rate. However, the elite japonica cultivar Koshihikari, which has a nonfunctional el1 allele for early flowering in long days, produces fertile spikelets and normal grain yields, like other elite japonica cultivars. This indicates that as-yet-unknown regulator(s) that can overcome the male sterile phenotype of the el1 mutation must have been introduced into Koshihikari.ConclusionsThe el1 mutation contributes to early flowering in japonica rice under long days but fails to limit GA signaling, thus negatively affecting spikelet fertility, which results in a loss of grain yield. Thus, EL1 is essential for photoperiod sensitivity in flowering as well as spikelet fertility in grain production.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-015-0058-1) contains supplementary material, which is available to authorized users.

Novel function of a putative MOC1 ortholog associated with spikelet number per spike in common wheat.

Axillary meristems play an important role in determining final plant architecture and floral structures. Tomato Ls, Arabidopsis LAS and rice MOC1 are orthologous genes regulating axillary meristem initiation and outgrowth. Their functions are generally conserved but the functional specificities are divergent among species. Obvious differences between rice panicles and wheat spikes suggest the divergent functions of MOC1 and its wheat ortholog. We show that TaMOC1 might be involved in wheat spikelet development. TaMOC1 is a typical nucleus localized protein with transcriptional activation abilities. The variable N-termini of TaMOC1 protein is necessary for transcriptional activation. TaMOC1 is highly expressed in ears with length of 2, 3 and 6 cm. Significant associations between the TaMOC1-7A haplotype and spikelet number per spike were observed in ten environments over 3 years and 2 sites. TaMOC1-7A HapH, a favored haplotype acquired during wheat polyploidization, may make a positive contribution to spikelet number per spike. Based on evolutionary analysis, geographic distribution and frequency changes, TaMOC1-7A HapH might be associated with wheat domestication and Chinese wheat breeding history. The pyramiding favorable alleles of TaMOC1-7A HapH and TaSnRK2.10 (C, associated with higher TGW) can improve both spikelet number per spike and TGW simultaneously.

Effects of 1-methylcyclopropene on function of flag leaf and development of superior and inferior spikelets in rice cultivars differing in panicle types

High ethylene production usually slackens spikelets development in compact panicled rice (Oryza sativa L.) cultivars. 1-Methylcyclopropene (1-MCP) is a potent inhibitor of ethylene action that has been shown to prevent ethylene-induced effects in fruits. However, effects of 1-MCP on spikelets development in rice cultivars differing in panicle types are unclear. This study explored whether 1-MCP is involved in regulating rice flag leaf function, and superior and inferior spikelets development. Four rice cultivars were field grown in 2012 and 2013, including two lax-panicled cultivars, Liangyoupeijiu (LYP9) and Guodao 6 (GD6), and two compact-panicled cultivars, Yongyou 9 (YY9) and Yongyou 12 (YY12). Results showed that 1-MCP played a positive role in regulating photosynthetic rate of rice flag leaf. Application of 1-MCP was more effective on enhancing grain filling rate of LYP9, GD6, and YY9. 1-Aminocyclopropane-1-carboxylic acid synthase (ACS) activity and ethylene production of inferior spikelets were more sensitive to the regulation of 1-MCP comparing to that in superior spikelets. Compared to other cultivars, ACS activity and ethylene production in inferior spikelets of LYP9 with 1-MCP treatment were significantly lower than that in control (CK). Effect of 1-MCP on starch content in superior and inferior spikelets varied with rice cultivars, but application of 1-MCP significantly enhanced starch content of inferior spikelets for LYP9. To compare with CK, application of 1-MCP greatly increased grain yield, spikelet fertility, and harvest index for LYP9, GD6, and YY9, especially for LYP9. Results indicate that 1-MCP favorably regulated flag leaf photosynthesis and inferior spikelets development in rice cultivars used in this trial, and LYP9 showed the best performances after application of 1-MCP.

Ppd-1 is a key regulator of inflorescence architecture and paired spikelet development in wheat.

The domestication of cereal crops such as wheat, maize, rice and barley has included the modification of inflorescence architecture to improve grain yield and ease harvesting(1). Yield increases have often been achieved through modifying the number and arrangement of spikelets, which are specialized reproductive branches that form part of the inflorescence. Multiple genes that control spikelet development have been identified in maize, rice and barley(2-5). However, little is known about the genetic underpinnings of this process in wheat. Here, we describe a modified spikelet arrangement in wheat, termed paired spikelets. Combining comprehensive QTL and mutant analyses, we show that Photoperiod-1 (Ppd-1), a pseudo-response regulator gene that controls photoperiod-dependent floral induction, has a major inhibitory effect on paired spikelet formation by regulating the expression of FLOWERING LOCUS T (FT)(6,7). These findings show that modulated expression of the two important flowering genes, Ppd-1 and FT, can be used to form a wheat inflorescence with a more elaborate arrangement and increased number of grain producing spikelets.

Overexpression of the JAZ factors with mutated jas domains causes pleiotropic defects in rice spikelet development

In a determinate meristem, such as a floral meristem, a genetically determined number of organs are produced before the meristem is terminated. In rice, iterative formation of organs during flower development with defects in meristem determinacy, classically called ‘proliferation’, is caused by several mutations and observed in dependence on environmental conditions. Here we report that overexpression of several JAZ proteins, key factors in jasmonate signaling, with mutations in the Jas domains causes an increase in the numbers of organs in florets, aberrant patterns of organ formation and repetitious organ production in spikelets. Our results imply that JAZ factors modulate mechanisms that regulate meristem functions during spikelet development.

Morphogenesis and Molecular Basis on the Unclosed Glumes, a Novel Mutation Related to the Floral Organ of Rice

The development of the rice floral organ directly affects rice yield and quality, and rice spikelet development has always been the hotspot in the field of botanical research. Mutants of the rice floral organ are very important intermediate materials which are used to reveal the genetic mechanism of spikelet development. In the present study, a stable rice mutant named unclosed glumes (ucgl) with a Japonica background, of which the lemma and palea cannot close fully after flowering, was isolated from the population mutagenized by using the ethyl methane sulfonate (EMS) in rice. Results from the genetic analysis indicated that the mutant was controlled by a single recessive gene. The UCGL locus was mapped to a 118-kb region between SSR makers R8UM89 and RM23258 on chromosome 8. There was a C to T substitution at the fifth exon of LOC_Os08g0459600 by sequencing analysis. LOC_Os08g0459600 encodes 12-oxo-phytodienoic acid reductase 7 (OPR7), which is one of the key enzymes in the jasmonic acid (JA) biosynthesis. RT-PCR analysis showed that the UCGL gene could be expressed in all of the tested tissues including roots, stems, leaves, and panicles. Also, the concentration of endogenous JA in the ucgl mutant was reduced in contrast to the wild-type. The expression levels of JA biosynthetic genes including OsLOX and OsAOS were significantly increased in the ucgl mutant plant. The expression of UCGL (OsOPR7) could regulate JA metabolism and affect the closure of glumes in rice. As far as we know, the UCGL is thus a new gene and has not been reported as controlling the closure of rice glumes, thusthe study of it could provide a new insight into the role of JA in rice floral morphological development.

Population genetics and phylogenetic analysis of the vrs1 nucleotide sequence in wild and cultivated barley.

Spike morphology is a key characteristic in the study of barley genetics, breeding, and domestication. Variation at the six-rowed spike 1 (vrs1) locus is sufficient to control the development and fertility of the lateral spikelet of barley. To study the genetic variation of vrs1 in wild barley (Hordeum vulgare subsp. spontaneum) and cultivated barley (Hordeum vulgare subsp. vulgare), nucleotide sequences of vrs1 were examined in 84 wild barleys (including 10 six-rowed) and 20 cultivated barleys (including 10 six-rowed) from four populations. The length of the vrs1 sequence amplified was 1536 bp. A total of 40 haplotypes were identified in the four populations. The highest nucleotide diversity, haplotype diversity, and per-site nucleotide diversity were observed in the Southwest Asian wild barley population. The nucleotide diversity, number of haplotypes, haplotype diversity, and per-site nucleotide diversity in two-rowed barley were higher than those in six-rowed barley. The phylogenetic analysis of the vrs1 sequences partially separated the six-rowed and the two-rowed barley. The six-rowed barleys were divided into four groups.

Jasmonic acid regulates spikelet development in rice

The spikelet is the basal unit of inflorescence in grasses, and its formation is crucial for reproductive success and cereal yield. Here, we report a previously unknown role of the plant hormone jasmonic acid (JA) in determining rice (Oryza sativa) spikelet morphogenesis. The extra glume 1 (eg1) and eg2 mutants exhibit altered spikelet morphology with changed floral organ identity and number, as well as defective floral meristem determinacy. We show that EG1 is a plastid-targeted lipase that participates in JA biosynthesis, and EG2/OsJAZ1 is a JA signalling repressor that interacts with a putative JA receptor, OsCOI1b, to trigger OsJAZ1's degradation during spikelet development. OsJAZ1 also interacts with OsMYC2, a transcription factor in the JA signalling pathway, and represses OsMYC2's role in activating OsMADS1, an E-class gene crucial to the spikelet development. This work discovers a key regulatory mechanism of grass spikelet development and suggests that the role of JA in reproduction has diversified during the flowering plant evolution.

OsmiR396d-Regulated OsGRFs Function in Floral Organogenesis in Rice through Binding to Their Targets OsJMJ706 and OsCR4

Inflorescence and spikelet development determine grain yields in cereals. Although multiple genes are known to be involved in the regulation of floral organogenesis, the underlying molecular network remains unclear in cereals. Here, we report that the rice (Oryza sativa) microRNA396d (OsmiR396d) and its Os Growth Regulating Factor (OsGRF) targets, together with Os Growth Regulating Factor-Interacting Factor1 (OsGIF1), are involved in the regulation of floral organ development through the rice JMJD2 family jmjC gene 706 (OsJMJ706) and crinkly4 receptor-like kinase (OsCR4). Transgenic knockdown lines of OsGRF6, a predicted target of OsmiR396d, and overexpression lines of OsmiR396d showed similar defects in floral organ development, including open husks, long sterile lemmas, and altered floral organ morphology. These defects were almost completely rescued by overexpression of OsGRF6. OsGRF6 and its ortholog OsGRF10 were the most highly expressed OsGRF family members in young inflorescences, and the grf6/grf10 double mutant displayed abnormal florets. OsGRF6/OsGRF10 localized to the nucleus, and electrophoretic mobility shift assays revealed that both OsGRF6 and OsGRF10 bind the GA response element in the promoters of OsJMJ706 and OsCR4, which were reported to participate in the regulation of floral organ development. In addition, OsGRF6 and OsGRF10 could transactivate OsJMJ706 and OsCR4, an activity that was enhanced in the presence of OsGIF1, which can bind both OsGRF6 and OsGRF10. Together, our results suggest that OsmiR396d regulates the expression of OsGRF genes, which function with OsGIF1 in floret development through targeting of JMJ706 and OsCR4. This work thus reveals a microRNA-mediated regulation module for controlling spikelet development in rice.

Evolution and Development of the Spikelet and Flower ofRhynchospora(Cyperaceae)

Premise of research. Rhynchospora, one of the biggest genera of sedges, displays several spikelet and flower modifications and is one of a few genera where the pollination strategy changes from wind to insect pollination; however, the mechanisms that have promoted such diversity in the genus are unknown. We have performed a comparative study of spikelet and flower development of Rhynchospora from an evolutionary perspective to get insight into the bases of spikelet and flower evolution. Particularly, we investigate correlations between the change from wind to insect pollination that occur in the genus and the spikelet and flower traits.Methodology. The spikelet and flower development of nine species of Rhynchospora were studied using SEM images. Parsimony, maximum likelihood, and Bayesian reconstruction analyses were conducted to evaluate the evolutionary history of flower and spikelet developmental programs.Pivotal results. We identified seven morphological and developmental traits that vary among Rhynchospora species; ancestral character reconstructions show that the spikelet and flower morphology and their developmental pathways support the diversification of Rhynchospora lineages.Conclusions. Our results suggest that the evolution of spikelet and flower developmental programs in Rhynchospora may be related to the evolution of its pollination type and mating system. The evolution toward a bisexual spikelet and flowers in which the androecium develops faster than the gynoecium may represent important steps for the transition from a wind- to insect-pollination system. In addition, we found new traits of spikelets and flowers that may help to distinguish natural groups within Rhynchospora.