SDG712, a Putative H3K9-Specific Methyltransferase Encoding Gene, Delays Flowering through Repressing the Expression of Florigen Genes in Rice

Siju Zhang,Hongjiao Hao,Yingying Li,Xuan Ma,Weiyin Liu,Weijiang Luan,Rui Zheng,Shanshan Liang,Xiaonan Liu

doi:10.1186/s12284-021-00513-9

Abstract

SET domain group (SDG) proteins have been identified to be involved in histone modification and participate in diverse biological processes. Rice contains 41 SDG genes, however, most of which have not been functionally characterized. Here, we report the identification and functional investigation of rice SDG712 gene. Phylogenic analysis revealed that SDG712 belongs to the H3K9-specific SDG subclade. SDG712 is highly expressed in leaves during reproductive growth stage with obvious circadian rhythmic pattern. Mutation of SDG712 promotes rice flowering, while overexpression of SDG712 delays rice flowering. Gene expression analysis suggested that SDG712 acts downstream of Hd1, while acts upstream of Ehd1, Hd3a and RFT1. Subcellular localization assay demonstrated that SDG712 is localized in the nucleus. Chromatin immunoprecipitation (ChIP) assay showed that the H3K9me2 levels at Hd3a and RFT1 loci were increased in SDG712 overexpression transgenic plants, indicating that SDG712 may mediate the H3K9 di-methylation on these loci to repress rice flowering. Taken together, our findings demonstrated that SDG712 is a negative flowering regulatory gene in rice, and it delays flowering through repressing key flowering regulator gene Ehd1 and the florigen genes Hd3a and RFT1.

Highlights

Rice is an important food crop worldwide, which supplies more than half of the world’s population
We focused on the gene LOC_Os02g40770, which encodes a putative methyltransferase and was designated as SDG712 in a previous phylogenetic study (Ng et al, 2007). qRT-PCR assay confirmed that the expression of SDG712 was significantly decreased in hd1–3 mutant compared with wild type under both SD and LD conditions (Fig. 1A, B), in agreement with the microarray result
Gene expression analysis revealed that the expression of Ehd1 and the florigen genes Hd3a and RFT1 were down-regulated in SDG712-OX plants, resulting in the down-regulation of floral identity gene MADS14

Summary

Introduction

Rice is an important food crop worldwide, which supplies more than half of the world’s population. Rice yield is restricted by various environmental factors, including photoperiod, temperature, nutrition, etc. Heading-date (or flowering time) is an important agronomic trait closely related to rice yield and regional adaptability; it is mainly modulated by photoperiodic signals and endogenous flowering regulatory genes. Rice is a facultative short-day (SD) plant, short-day induces the flowering while long-day (LD) represses the flowering. With the development of molecular genetics, The expression of florigen genes are mainly regulated by several critical genes under SD and LD conditions.

Methods

Results

Conclusion