Shirong Zhou, Shanshan Zhu, Song Cui, Haigang Hou, Haoqin Wu, Benyuan Hao, Liang Cai, Zhuang Xu, Linglong Liu, Ling Jiang, Haiyang Wang, Jianmin Wan

New Phytol. Journal; 2021 May;230(3):943-956.  doi: 10.1111/nph.17158. 

Abstract

Rice is a facultative short day (SD) plant. In addition to serving as a model plant for molecular genetic studies of monocots, rice is a staple crop for about half of the world's population. Heading date is a critical agronomic trait, and many genes controlling heading date have been cloned over the last 2 decades. The mechanism of flowering in rice from recognition of day length by leaves to floral activation in the shoot apical meristem has been extensively studied. In this review, we summarise current progress on transcriptional and post-transcriptional regulation of heading date in rice, with emphasis on post-translational modifications of key regulators, including Heading date 1 (Hd1), Early heading date 1 (Ehd1), Grain number, plant height, and heading date7 (Ghd7). The contribution of heading date genes to heterosis and the expansion of rice cultivation areas from low-latitude to high-latitude regions are also discussed. To overcome the limitations of diverse genetic backgrounds used in heading date studies and to gain a clearer understanding of flowering in rice, we propose a systematic collection of genetic resources in a common genetic background. Strategies in breeding adapted cultivars by rational design are also discussed.

See: https://pubmed.ncbi.nlm.nih.gov/33341945/

Fig.1: Genetic pathways controlling heading date in rice. Schematic representation of genetic pathways controlling flowering in rice. A circadian clock is shown at the top. Key heading date genes are indicated in oval backgrounds. Arrows indicate upregulation, and bars indicate downregulation. Rice has two florigen genes, Hd3a and RFT1, short day (SD) conditions accelerate heading by promoting the expression of Hd3a through Hd1 and Ehd1. Expression of Ehd1 can be upregulated or downregulated by many genes. Hd1 can be activated by OsGI under SD conditions. In long day (LD) conditions, Hd1 function reverses to flowering inhibition; this reversal is controlled by many other factors such as Ghd7 and DTH8 and is mediated by protein–protein interactions. The florigen proteins Hd3a and RFT1 are transported to the shoot apical meristem (SAM) after induction in the leaves. In the SAM, they form the florigen activation complex (FAC), and activate the expression of downstream targets, including members of MADS-box transcription factor family genes that control phase transition of the SAM from vegetative to reproductive development. FAC and repressive FAC-like complexes can also be formed in the SAM and leaves to fine tune the heading date.