Academic literature on the topic 'Sterile lemma'

Hull opening is a key physiological process during reproductive development, strongly affecting the subsequent fertilization and seed development in rice. In this study, we characterized a rice mutant, non-open hull 1 (noh1), which was derived from ethylmethane-sulfonate (EMS)-treated Xinong 1B (Oryza sativa L.). All the spikelets of noh1 developed elongated and thin lodicules, which caused the failure of hull opening and the cleistogamy. In some spikelets of the noh1, sterile lemmas transformed into hull-like organs. qPCR analysis indicated that the expression of A- and E-function genes was significantly upregulated, while the expression of some B-function genes was downregulated in the lodicules of noh1. In addition, the expression of A-function genes was significantly upregulated, while the expression of some sterile-lemma maker genes was downregulated in the sterile lemma of noh1. These data suggested that the lodicule and sterile lemma in noh1 mutant gained glume-like and lemma-like identity, respectively. Genetic analysis showed that the noh1 trait was controlled by a single recessive gene. The NOH1 gene was mapped between the molecular markers ZJ-9 and ZJ-25 on chromosome 1 with a physical region of 60 kb, which contained nine annotated genes. These results provide a foundation for the cloning and functional research of NOH1 gene.

SUMMARYFloral organ development influences plant reproduction and crop yield. The mechanism of floral organ specification is generally conserved in angiosperms as demonstrated by the ‘ABC’ model. However, mechanisms underlying the development of floral organs in specific groups of species such as grasses remain unclear. In the genus Oryza (rice), a spikelet consists of a fertile floret sub-tended by a lemma, a palea, two sterile lemmas and rudimentary glumes. To understand how the lemma is formed, a curve-shaped lemma-distortion1 (ld1) mutant was identified. Genetic analysis confirmed that the ld1 mutant phenotype was due to a single recessive gene mutation. Using a large F2 population, the LD1 gene was mapped between markers Indel-7-15 and Indel-7-18, which encompassed a region of 15·6 kilo base pairs (kbp). According to rice genome annotations, two putative genes, LOC_Os07g32510 and LOC_Os07g32520, were located in this candidate region. However, DNA sequencing results indicated only 1 base pair (bp) substitution (T⇨C) was found in LOC_Os07g32510 between the wild-type and the ld1 mutant. Thus LOC_Os07g32510, encoding a DNA binding with one zinc finger (DoF) containing protein, was the candidate gene for LD1. Further analysis showed that mutation of the amino acid cysteine (C) to arginine (R) was likely to lead to zinc finger protein deactivation. Phylogenetic and conservation analysis of the gene from different species revealed that cysteine was critical to LD1 function. As a new gene controlling lemma development, the study of LD1 could provide insights into rice floral organ formation mechanisms.

The spikelet is a unique inflorescence structure in grass. The molecular mechanisms behind the development and evolution of the spikelet are far from clear. In this study, a dominant rice mutant, lateral florets 1 (lf1), was characterized. In the lf1 spikelet, lateral floral meristems were promoted unexpectedly and could generally blossom into relatively normal florets. LF1 encoded a class III homeodomain-leucine zipper (HD-ZIP III) protein, and the site of mutation in lf1 was located in a putative miRNA165/166 target sequence. Ectopic expression of both LF1 and the meristem maintenance gene OSH1 was detected in the axil of the sterile lemma primordia of the lf1 spikelet. Furthermore, the promoter of OSH1 could be bound directly by LF1 protein. Collectively, these results indicate that the mutation of LF1 induces ectopic expression of OSH1, which results in the initiation of lateral meristems to generate lateral florets in the axil of the sterile lemma. This study thus offers strong evidence in support of the “three-florets spikelet” hypothesis in rice.

The characterization of rice (Oryza sativa L.) landraces enables to identify phenotypically unique variables which certainly aid in rice breeding program. So, an experiment was conducted in alpha designed to characterize 188 rice landraces from NAGRC (National Agriculture Genetic Resources center) Nepal for their qualitative agromorphologies in research farm of Agriculture and Forestry University (AFU), Rampur, Chitwan in 2020 AD. Twenty-nine qualitative variables viz; twelve leaf characters, six culm characters, four panicle character and seven grain characters were observed and 26 characters revealed diverse trait expressions for each variable in experimented 188 rice accessions. Two leaf characters namely ligule colour and flag leaf attitude for early observation and one grain character (stigma colour for early observation) showed no variation among studied rice accessions. The intensity of green colour of leaf blade, culm lodging resistance and culm habit, secondary branching of panicle, and lemma and palea colour, lemma apiculus colour and sterile lemma colour, elucidated the higher variation in studied characters. The distinction revealed in qualitative characters approves the presence of abundant phenotypic diversity in the landraces assemblage and that eventually signifies the efficient and effective utilization of landrace in rice breeding programs.

Flowering material of Ferrocalamus rimosivaginus has been identified, allowing its analysis and description. The unit of inflorescence of the synflorescences of F. rimosivaginus is panicle-like and its fruit is berry-like. Ferrocalamus rimosivaginus differs from F. strictus in its rachilla puberulent except on its adaxial surface, the first glume with a glabrous apex, the abaxially glabrous lemma with an acute mucronate apex, and the palea with the surfaces between keels apically pubescent and progressively less pubescent towards the glabrous base. An epitype is designated to support the sterile holotype.

Studies on meristem identity regulators in Rice (Oryza sativa), a model plant for cereal crops have revealed how meristem identity and transitions are controlled, bearing implications for crop yield improvement. We were interested in exploring the function of OsULTRAPETALA1 (OsULT1), whose Arabidopsis homolog is a TrxG Factor, in rice inflorescence and spikelet/floret organ development. OsULT1 is a direct downstream target of floret meristem identity and development transcriptional regulator OsMADS1 (Khanday et al., 2016). The aim of this thesis is to functionally characterize OsULT1 by raising transgenic rice plants with ubiquitous knockdown and other lines that are overexpressors of OsULT1. In the dsRNAi-OsULT1 knockdown transgenics, we observed reduced plant height, panicle branching, and delay in flowering time. Interestingly, the pUbi-OsULT1 overexpression transgenics showed a converse phenotype of precocious flowering. Histological studies on young branching inflorescence meristem from the dsRNAi-OsULT1 knockdown transgenics and wild-type plants, was done to understand the onset of developmental abnormalities during panicle development. We observed an increase in the number of lateral organs made from the spikelet meristem; this could be due to a delay in SM to FM transition. These data suggest OsULT1 to be a heterochronic factor regulating meristem progression. Histological analyses of young spikelets showed a homeotic conversion of sterile lemma to a lemma-like organ. In floral meristem of knockdown plants, reduced palea and altered stamen number were noted. We quantified expression levels of some selected well-studied spikelet meristem regulators. qRT-PCR done on RNA from pooled dsRNAi-OsULT1 panicle tissues (Early-stage: 0.1 to 0.3cm and Late-stage: 0.4 to 2cm) and compared to similarly staged wild-type panicles. We found OsMADS1 and OsIDS1 transcript levels to be up-regulated and down-regulated respectively in the dsRNAi-OsULT1 transgenics compared to the wild-type. This could relate to the sterile lemma and rudimentary glume phenotypes observed in the affected knockdown spikelets. Since chromatin modifiers lacking DNA-binding domain recruit TF’s to target genes, we tested the possibility of protein interaction between OsULT1 and OsMADS1 using the yeast two-hybrid assay. This assay confirmed the interaction between OsULT1 and OsMADS1, thus raising the prospect of such a TF–Chromatin factor complex regulating downstream target gene expression by modulation of the histone modification status of the gene loci relevant for SM and FM development. We surveyed the abundance of repressive and activating histone marks in two developmental stages in wild-type panicle tissues as an attempt to correlate histone marks with transcript abundance. We observed as expected an inverse correlation between the expression levels of OsMADS34 and OsMADS22 and the abundance of the H3K27me3 mark at these two loci. We then evaluated the chromatin status at the genes which are differentially expressed in the dsRNAi-OsULT transgenics like OsMADS1, OsIG1, and OsIDS1. The results of the ChIP-qPCR analysis to assess the abundance of histone marks indicate a complex relationship between chromatin marks and transcript abundance. For future in-depth studies of gene targets in specific stages of SM and FM, we have standardized Laser Capture Micro-dissection of specific rice wild-type panicle meristems for transcriptomic studies in these recessed difficult to access tissues. Preliminary data indicate sets of transcripts that could be specific to Primary Branch Meristem (PBM), Secondary Branch Meristem (SBM), and Floral Meristem (FM). Overall, we have used reverse genetics tools to elucidate the functions of a predicted Trithorax-Group factor OsULT1 in spikelet meristem transient maintenance, its lateral organ development, and effects on floret organ numbers. The implications of the studies support the published hypothesis that ancestral rice species had three-fertile floret per spikelet (Ren et al., 2020; Zhang et al., 2017), instead of the one floret per spikelet in seen in extant species. The work in this thesis highlights the important role of chromatin modifiers like the Trithorax factors in rice panicle development.