RL99 Was Essential for High Yield Formation by Regulating Leaf Morphogenesis and Root Development in Rice

Rice (Oryza sativa L.) is the world’s most important food crop. Rice cultivars with high yield are good objects to further explore yield potential for feeding tremendous world populations. In this study, a γ-irradiation-induced mutant rl99 obtained from Zhejing 99 demonstrated serious rolling leaves and shortened adventitious roots. Exogenously applying low concentration of BR has no promotion on any root growth of either the wild type or the mutant, whereas high concentrations of BR repressed the length of the adventitious roots of the rl99 mutant. This is the first report about exogenous BR inhibition on the adventitious roots in rice. The gene RL99 (LOC_Os07g03450) was map-based cloned and allelic to the reported gene NAAL1/CRL6/CHR729/OsCHR4. This was the first report about the leaf-rolling trait performed by the gene. As a chromatin remodeling factor, the CHD protein RL99 was not detected using the yeast two-hybrid experiment to interact with AS1/AS2 homologous in rice, as a protein related to the KNOX family in Arabidopsis. In all, the low yield of the mutant owed to serious leaf rolling with decreased bulliform cells and abnormal chloroplast structure with increased osmiophilic granules, decreased starch grains, and shortened adventitious roots with unclear BR homeostasis mechanism. Therefore, this research gives a clue to exploring high yield in rice and to better ensure the food security of the world.