Analysis of co-expression and gene regulatory networks associated with sterile lemma development in rice

BACKGROUND

The 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.

RESULTS

In 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.

CONCLUSION

The 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.

The C2H2 zinc-finger protein LACKING RUDIMENTARY GLUME 1 regulates spikelet development in rice

Rice (Oryza sativa) spikelets are a unique inflorescence structure and their development directly determines grain size and yield. Although many genes related to spikelet development have been reported, the molecular mechanisms underlying this process have not been fully elucidated. In this study, we identified a new recessive rice mutant, lacking rudimentary glume 1 (lrg1). The lrg1 spikelets only formed one rudimentary glume, which, along with the sterile lemmas, was homeotically transformed into lemma-like organs and acquired lemma identity. The transition from the spikelet to the floral meristem was delayed in the lrg1 mutant, resulting in the formation of an ectopic lemma-like organ between the sterile lemma and the terminal floret. In addition, we found that the abnormal lrg1 grain phenotype resulted from the alteration of cell numbers and the hull size. LRG1 encodes a ZOS4-06-C2H2 zinc-finger protein with the typical EAR motifs, and is expressed in all organs and tissues. LRG1 localizes to the nucleus and can interact with the TOPLESS-RELATED PROTEINs (TPRs) to repress the expressions of their downstream target genes. Taken together, our results reveal that LRG1 plays an important role in the regulation of spikelet organ identity and grain size.