RLB (RICE LATERAL BRANCH) recruits PRC2-mediated H3K27 tri-methylation on OsCKX4 to regulate lateral branching

Abstract

Lateral branches such as shoot and panicle are determining factors and target traits for rice (Oryza sativa L.) yield improvement. Cytokinin promotes rice lateral branching; however, the mechanism underlying the fine-tuning of cytokinin homeostasis in rice branching remains largely unknown. Here, we report the map-based cloning of RICE LATERAL BRANCH (RLB) encoding a nuclear-localized, KNOX-type homeobox protein from a rice cytokinin-deficient mutant showing more tillers, sparser panicles, defected floret morphology as well as attenuated shoot regeneration from callus. RLB directly binds to the promoter and represses the transcription of OsCKX4, a cytokinin oxidase gene with high abundance in panicle branch meristem. OsCKX4 over-expression lines phenocopied rlb, which showed upregulated OsCKX4 levels. Meanwhile, RLB physically binds to Polycomb repressive complex 2 (PRC2) components OsEMF2b and co-localized with H3K27me3, a suppressing histone modification mediated by PRC2, in the OsCKX4 promoter. We proposed that RLB recruits PRC2 to the OsCKX4 promoter to epigenetically repress its transcription, which suppresses the catabolism of cytokinin, thereby promoting rice lateral branching. Moreover, antisense inhibition of OsCKX4 under the LOG promoter successfully increased panicle size and spikelet number per plant without affecting other major agronomic traits. This study provides insight into cytokinin homeostasis, lateral branching in plants, and also promising target genes for rice genetic improvement.

Melatonin Mediates Axillary Bud Outgrowth by Improving Nitrogen Assimilation and Transport in Rice

“…In the CK pathway, the expression of OsLOGL5 and OsLOGL10 increased upon treatment with 1.5 mm Lys + 0.5 mm Arg + 1 μm melatonin, whereas that of OsCKX4 was only induced upon treatment with 10 μm melatonin compared to other treatments ( Figure 5D ). Previous reports suggest that both OsLOGL5 ( Hou et al, 2021a ) and OsCKX4 ( Wang et al, 2022a ) regulate the elongation of axillary buds in rice.…”

Genetic and molecular factors in determining grain number per panicle of rice

“…The application of these MPPs provide higher mapping power and resolution in exploring genetic architecture of yield traits in rice ( Zaw et al, 2019 ; Han et al, 2020 ; Ayaad et al, 2021 ; Huerta et al, 2021 ), and would be effective strategies in the cloning of GN-associated genes and rice breeding. In addition, current studies also shed light on the roles of epigenetic modification related genes in GN regulation ( Zhang et al, 2017 ; Wang et al, 2022a ). Despite the increasing attention on the importance of epigenetic regulations in plant growth, stress response, and crop yield ( Lu et al, 2018 , 2020 ), the significance and mechanisms of epigenetic modification related genes in GN regulation remains largely elusive.…”

Genetic and molecular pathways controlling rice inflorescence architecture

“…Overexpression of OsCKX4 also leads to changes in inflorescence architecture as demonstrated by sparser and smaller panicles ( Wang et al., 2022 ). The KNOX protein RICE LATERAL BRANCH (RLB)/OSH15 epigenetically suppresses OsCKX4 expression through recruiting OsEMF2b, a component of the polycomb repressive complex 2 (PRC2) which mediates H3K27 tri-methylation on target genes.…”

“…The KNOX protein RICE LATERAL BRANCH (RLB)/OSH15 epigenetically suppresses OsCKX4 expression through recruiting OsEMF2b, a component of the polycomb repressive complex 2 (PRC2) which mediates H3K27 tri-methylation on target genes. The loss-of-function mutant rlb has shorter inflorescences with reduced spikelets, due to the decrease of secondary branches ( Wang et al., 2022 ).…”