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The homeotic gene long sterile lemma (G1) specifies sterile lemma identity in the rice spikelet.

ABSTRACT: The mechanism of floral organ specification is principally conserved in angiosperms, as demonstrated by the ABC model. By contrast, mechanisms that regulate the development of organs or structures specific to a group of species remain unclear. Grasses have unique inflorescence units, comprising spikelets and florets. In the genus Oryza (rice), the single spikelet consists of a fertile floret subtended by a lemma and a palea, two sterile lemmas, and rudimentary glumes. Each sterile lemma is a tiny glume-like organ with a smooth surface. Here, we have examined a long sterile lemma1 (g1) mutant, in which the sterile lemma is enlarged like the lemma. Detailed phenotypic analysis reveals that the large sterile lemma in the g1 mutant appears to be caused by homeotic transformation of the sterile lemma into a lemma, suggesting that G1 is involved in the repression of lemma identity to specify the sterile lemma. Gene isolation reveals that G1 is a member of a plant-specific gene family that encodes proteins with a previously uncharacterized domain, named here ALOG (Arabidopsis LSH1 and Oryza G1). G1 mRNA is expressed in sterile lemma primordia throughout their development, and G1 protein is localized in the nucleus. A trans-activation assay using the yeast GAL4 system suggests that G1 is involved in transcriptional regulation. Repression of lemma identity by G1 is consistent with a hypothesis proposed to explain the morphological evolution of rice spikelets. We also show that a wild rice species, Oryza grandiglumis, that forms large sterile lemmas has serious mutations in the G1 gene.

SUBMITTER: Yoshida A

PROVIDER: S-EPMC2775035 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Cloning of long sterile lemma (lsl2), a single recessive gene that regulates spike germination in rice (Oryza sativa L.).

Project description:BackgroundRice is a typical monocotyledonous plant and an important cereal crop. The structural units of rice flowers are spikelets and florets, and floral organ development and spike germination affect rice reproduction and yield.ResultsIn this study, we identified a novel long sterile lemma (lsl2) mutant from an EMS population. First, we mapped the lsl2 gene between the markers Indel7-22 and Indel7-27, which encompasses a 25-kb region. The rice genome annotation indicated the presence of four candidate genes in this region. Through gene prediction and cDNA sequencing, we confirmed that the target gene in the lsl2 mutant is allelic to LONG STERILE LEMMA1 (G1)/ELONGATED EMPTY GLUME (ELE), hereafter referred to as lsl2. Further analysis of the lsl2 and LSL2 proteins showed a one-amino-acid change, namely, the mutation of serine (Ser) 79 to proline (Pro) in lsl2 compared with LSL2, and this mutation might change the function of the protein. Knockout experiments showed that the lsl2 gene is responsible for the long sterile lemma phenotype. The lsl2 gene might reduce the damage induced by spike germination by decreasing the seed germination rate, but other agronomic traits of rice were not changed in the lsl2 mutant. Taken together, our results demonstrate that the lsl2 gene will have specific application prospects in future rice breeding.ConclusionsThe lsl2 gene is responsible for the long sterile lemma phenotype and might reduce the damage induced by spike germination by decreasing the seed germination rate.

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FZP determines grain size and sterile lemma fate in rice.

Project description:In grass, the spikelet is a unique inflorescence structure that directly determines grain yield. Despite a great deal of research, the molecular mechanisms behind spikelet development are not fully understood. In the study, FZP encodes an ERF domain protein, and functions in grain size and sterile lemma identity. Mutation of FZP causes smaller grains and degenerated sterile lemmas. The small fzp-12 grains were caused by a reduction in cell number and size in the hulls. Interestingly, the sterile lemma underwent a homeotic transformation into a rudimentary glume in the fzp-12 and fzp-13 mutants, whereas the sterile lemma underwent a homeotic transformation into a lemma in FZP over-expressing plants, suggesting that FZP specifically determines the sterile lemma identity. We confirmed the function of FZP by complementation, CRISPR-Cas9 gene editing, and cytological and molecular tests. Additionally, FZP interacts specifically with the GCC-box and DRE motifs, and may be involved in regulation of the downstream genes. Our results revealed that FZP plays a vital role in the regulation of grain size, and first provides clear evidence in support of the hypothesis that the lemma, rudimentary glume, and sterile lemma are homologous organs.

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Project description:BackgroundThe sterile lemma is a unique organ of the rice (Oryza sativa L.) spikelet. However, the characteristics and origin of the rice sterile lemma have not been determined unequivocally, so it is important to elucidate the molecular mechanism of the development of the sterile lemma.ResultsIn the paper, we outline the regulatory mechanism of sterile lemma development by LONG STERILE LEMMA1 (G1), which has been identified as the gene controlling sterile lemma development. Based on the comprehensive analyses of transcriptome dynamics during sterile lemma development with G1 alleles between wild-type (WT) and mutant (MT) in rice, we obtained co-expression data and regulatory networks related to sterile lemma development. Co-transfection assays of rice protoplasts confirmed that G1 affects the expression of various phytohormone-related genes by regulating a number of critical transcription factors, such as OsLBD37 and OSH1. The hormone levels in sterile lemmas from WT and MT of rice supports the hypotheses that lower auxin, lower gibberellin, and higher cytokinin concentrations are required to maintain a normal phenotype of sterile lemmas.ConclusionThe regulatory networks have considerable reference value, and some of the regulatory relationships exhibiting strong correlations are worthy of further study. Taken together, these work provided a detailed guide for further studies into the molecular mechanism of sterile lemma development.

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