The rice HGW gene encodes a ubiquitin-associated (UBA) domain protein that regulates heading date and grain weight.

Juan Li,Qifa Zhang,Tongmin Mou,Jian Xu,Huangwei Chu,Yonghong Zhang,Changyin Wu,Keqiang Wu

doi:10.1371/journal.pone.0034231

Juan Li, Qifa Zhang + Show 6 more

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https://doi.org/10.1371/journal.pone.0034231

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Abstract

Heading date and grain weight are two determining agronomic traits of crop yield. To date, molecular factors controlling both heading date and grain weight have not been identified. Here we report the isolation of a hemizygous mutation, heading and grain weight (hgw), which delays heading and reduces grain weight in rice. Analysis of hgw mutant phenotypes indicate that the hemizygous hgw mutation decreases latitudinal cell number in the lemma and palea, both composing the spikelet hull that is known to determine the size and shape of brown grain. Molecular cloning and characterization of the HGW gene showed that it encodes a novel plant-specific ubiquitin-associated (UBA) domain protein localized in the cytoplasm and nucleus, and functions as a key upstream regulator to promote expressions of heading date- and grain weight-related genes. Moreover, co-expression analysis in rice and Arabidopsis indicated that HGW and its Arabidopsis homolog are co-expressed with genes encoding various components of ubiquitination machinery, implying a fundamental role for the ubiquitination pathway in heading date and grain weight control.

Highlights

Rice (Oryza sativa L.) is one of the most important food crops worldwide and a model for genetic and genomic researches in cereals [1,2,3]
We found that the heading date of this mutant was about 20 days later in natural field condition compared with wild type (WT) control (Figure 1F, G and H), but the numbers of panicle per plant and the numbers of grains per main panicle were not affected
In hgw mutant, the overall circumference of outer parenchyma cell layer of lemma and palea was reduced by 23% (19% and 23% for lemma and palea, respectively) when compared to the WT control (Figure 2E), suggesting defects in cell division and/or cell elongation

Summary

Introduction

Rice (Oryza sativa L.) is one of the most important food crops worldwide and a model for genetic and genomic researches in cereals [1,2,3]. Heading date (Ehd1), a flowering time gene unique to rice, encodes a B-type response regulator promoting floral transition preferentially under SD conditions, even in the absence of functional alleles of Hd1 [13]. Expression analysis revealed that Ehd functions upstream of Hd3a and RFT1 [13], whereas under LD conditions, transcription of Ehd and Hd3a but not Hd1 is repressed by Ghd7 [14], which encodes a CCT domain protein and has major effects on an array of traits in rice, including number of grains per panicle, plant height and heading date. Genes known to be involved in flowering time regulation, especially RFT homologs and those in the Ehd1/Hd3a pathway, are reduced to an undetectable level in these mutants [15,16], suggesting that RID1/Ehd acts as the master switch for the transition from the vegetative to reproductive phase, and promotes flowering upstream the photoperiod pathway in rice

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