The grass spikelet is a unique inflorescence structure that determines grain size. Although many genetic factors have been well characterized for grain size and glume development, the underlying molecular mechanisms in rice are far from established. Here, we isolated rice gene, AGL1 that controlled grain size and determines the fate of the sterile lemma. Loss of function of AGL1 produced larger grains and reduced the size of the sterile lemma. Larger grains in the agl1 mutant were caused by a larger number of cells that were longer and wider than in the wild type. The sterile lemma in the mutant spikelet was converted to a rudimentary glume-like organ. Our findings showed that the AGL1 (also named LAX1) protein positively regulated G1 expression, and negatively regulated NSG1 expression, thereby affecting the fate of the sterile lemma. Taken together, our results revealed that AGL1 played a key role in negative regulation of grain size by controlling cell proliferation and expansion, and supported the opinion that rudimentary glume and sterile lemma in rice are homologous organs.

Increasing tiller number is a target of high-yield rice breeding. Identification of tiller-defect mutants and their corresponding genes is helpful for clarifying the molecular mechanism of rice tillering. Summarizing research progress on the two processes of rice tiller formation, namely the formation and growth of axillary meristem, this paper reviews the effects of genetic factors, endogenous hormones, and exogenous environment on rice tillering, finding that multiple molecular mechanisms and signal pathways regulating rice tillering cooperate rice tillering, and discusses future research objectives and application of its regulatory mechanism. Elucidation of theis mechanism will be helpful for breeding high-yielding rice cultivars with ideal plant type via molecular design breeding.

Xanthine dehydrogenase, a member of the molybdenum enzyme family, participates in purine metabolism and catalyzes the generation of ureides from xanthine and hypoxanthine. However, the mechanisms by which xanthine dehydrogenase affects rice growth and development are poorly understood. In the present study, we identified a mutant with early leaf senescence and reduced tillering that we named early senescence and less-tillering 1 (esl1). Map-based cloning revealed that ESL1 encodes a xanthine dehydrogenase, and it was expressed in all tissues. Chlorophyll content was reduced and chloroplast maldevelopment was severe in the esl1 mutant. Mutation of ESL1 led to decreases in allantoin, allantoate, and ABA contents. Further analysis revealed that the accumulation of reactive oxygen species in esl1 resulted in decreased photosynthesis and impaired chloroplast development, along with increased sensitivity to abscisic acid and abiotic stresses. Ttranscriptome analysis showed that the ESL1 mutation altered the expression of genes involved in the photosynthesis process and reactive oxygen species metabolism. Our results suggest that ESL1 is involved in purine metabolism and the induction of leaf senescence. These findings reveal novel molecular mechanisms of ESL1 gene-mediated plant growth and leaf senescence.