OsSPL9 Regulates Grain Number and Grain Yield in Rice.

Li Hu,Shigui Li,Junjie Yin,Xiaoling Li,Hua Yuan,Xiaobo Zhu,Cheng Zhang,Weilan Chen,Ling Zheng,Bin Tu,Peng Qin,Wen Yang,Xiaoyu Zhang,Yuping Wang,Bingtian Ma

doi:10.3389/fpls.2021.682018

Abstract

Rice grain yield consists of several key components, including tiller number, grain number per panicle (GNP), and grain weight. Among them, GNP is mainly determined by panicle branches and spikelet formation. In this study, we identified a gene affecting GNP and grain yield, OsSPL9, which encodes SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) family proteins. The mutation of OsSPL9 significantly reduced secondary branches and GNP. OsSPL9 was highly expressed in the early developing young panicles, consistent with its function of regulating panicle development. By combining expression analysis and dual-luciferase assays, we further confirmed that OsSPL9 directly activates the expression of RCN1 (rice TERMINAL FLOWER 1/CENTRORADIALIS homolog) in the early developing young panicle to regulate the panicle branches and GNP. Haplotype analysis showed that Hap3 and Hap4 of OsSPL9 might be favorable haplotypes contributing to high GNP in rice. These results provide new insights on high grain number breeding in rice.

Highlights

Rice is a staple food and provides energy for more than half of the population in the world
Compared with R498, the plant height of lgn5 was reduced by 7.6% (Figures 1A,I), but there was no significant difference in the tiller number and panicle length of lgn5 (Figures 1B,J,K)
There was no significant difference in the number of primary branches; the number of secondary branches was significantly reduced by 41.7%, leading to a 54.7% reduction in grain number per panicle (GNP) (Figures 1C,D,L–N)

Summary

Introduction

Rice is a staple food and provides energy for more than half of the population in the world. Grain number per panicle (GNP) is an important factor determining grain yield and is associated with panicle branches and spikelet formation in rice. Gn1a (Grain number 1a), encoding a cytokinin oxidase, negatively regulates cytokinin accumulation in inflorescence meristems and the number of reproductive organs (Ashikari et al, 2005). Rice TERMINAL FLOWER 1/CENTRORADIALIS homologs, RCN1 and RCN2, play important roles in controlling the timing of phase transition. Overexpression of these two genes delays transition from the branch shoot to the floral meristem state and causes the formation of higher-order branches (Nakagawa et al, 2002). FZP (FRIZZLE PANICLE) controls the transition from panicle branches to spikelet formation by negatively regulating APO2 (RFL/ABERRANT PANICLE ORGANIZATION 2) and positively regulating the related

Methods

Results

Conclusion