International Journal on Agriculture Research and Environmental Sciences (IJARES)

Opinion Volume2-Issue2

The Genetic Regulations of Grain Weight Exist Extensive Diversity in Rice

Xiaoxiao Deng, Yangsheng Li*

State Key Laboratory of Hybrid Rice, Wuhan University, China

*Corresponding author: Yangsheng Li, State Key Laboratory of Hybrid Rice, Key laboratory for Research and Utilization of Heterosis in Indica Rice, Ministry of Agriculture, College of Life Sciences, Wuhan University, Wuhan, China
Article History
Received: August 10, 2021 Accepted: August 13, 2021 Published: August 16, 2021
Citation: Deng X, Yangsheng L. The Genetic Regulations of Grain Weight Exist Extensive Diversity in Rice. Int J. Agri Res Env Sci. 2021;2(2):33‒34. DOI:10.51626/ijares.2021.02.00011

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Opinion

Rice is one of the most important cereal crops in the world and feeding nearly half the world population [1]. Rice has been domesticated by humans for more than 10,000 years [2]. From 50°N to 40°S , from sea level and below to 3000m above sea level, various types of rice varieties are cultivated in 117 countries and regions. More than 400,000 rice accessions are kept in the germplasm banks in IRRI, China, India, the United States, Thailand, Japan, etc. Numerous variations reveal not only the phenotypic diversity for its adaptation to environments, but also genetic diversity within a species genome [3,4]. This opinion will focus on genetic diversity of grain weight in rice.

The grain weight is largely controlled by grain shape, including grain length, grain width and grain thickness, and degree of filling [5]. Regulation of grain weight is an important strategy for improving rice yield. In the past few decades, QTL mapping of grain weight by different genetic population has identified a large number of QTLs [6]. Meta-analysis of QTLs unravels consensus and stable QTLs by merging different QTLs from independent experiments regardless of their genetic backgrounds, population types, evaluated locations and years [7]. Meta-analysis is used to narrow down the candidate regions of QTLs and improve the confidence and accurate of QTLs. A study merge 339 grain weight QTLs published from 1996 to 2019 into 34 Meta-QTLs, which indicate the grain weight, as a complex quantitative traits, is controlled by numerous genetic locus in rice [7].

More than 100 genes affecting grain weight have been cloned in rice
(http://www.ricedata.cn/ontology/ontology.aspx?ta=TO:0000592), such as GS3 (Fan et al.), GW2 [8], TGW6 [9], GW6a [10], qTGW3 [11-13], which are beneficial to establish fundamental regulation networks controlling the traits. The molecular machines determining grain weight are involved in several important biological pathways, such as G protein signaling, the mitogen-activated protein kinase signaling pathway, the ubiquitin–proteasome pathway, phytohormone signalings, transcriptional regulation, photosynthesis, epigenetic modifications and microRNAs in rice [14,15]. GS3, DEP1, RGB1, and D1 are involving in G-protein regulation pathways; OsMKK10, OsMKK4, OsMAPK6, GSN1, and OsRAC1 are participating in mitogen activated protein kinase signaling pathway; GSK2, GW5, GL3, GS5, OsBAK1, OsWRK53, and XIAO are referring to Brassinosteroids signaling pathways; TGW6, OsARF4, and BG1 are taking part in auxin signaling pathways [14]. Recently, several new grain weight regulation pathways have been found, it is regulated by the miR167a-OsARF6-OsAUX3 pathway [16] and the GW2-WG1-OsbZIP47 pathway in rice [17]. Therefore, the regulation network and signaling pathways involving in grain weight indicate further a variety of molecular regulation mechanisms existing in rice.

The genomic variation in 3,010 diverse accessions of Asian cultivated rice have been analyzed to identify 29 million single nucleotide polymorphisms, 2.4 million small indels and over 90,000 structural variations that contribute to within- and between-population variation [18]. Using pan-genome analyses, more than 10,000 novel full-length protein-coding genes and a high number of presence–absence variations were identified [18], and furthermore, the hidden structural variations (SVs) and gene copy number variations (gCNVs) were discovered, and SVs and gCNVs had shaped gene expression profiles and agronomic trait variations [4]. Indica subspecies and japonica subspecies differ substantially both in genotype and phenotype. Some grain weight genes played a vital role in regulating grain weight. For example, Gn1a and GS3 play a key role on grain weight for heavy panicle-type rice Shuhui498 (R498) [18]. A major QTL GL3.3 was detected using a RIL population derived from indica-japonica cross. The combination of GL3.3 and GS3 resulted in extra-long grains in rice duo to GL3.3 interacting epistatically with GS3 [13]. In our study, the extensive diversity of grain weight existed in the RIL population derived from Luohui 9 (indica) and RPY geng (japonica) while there was little difference of the grain weight between the parents, but Luohui 9 and RPY geng revealed substantial differences in the whole genome, as well as the known grain weight genes (unpublished). It is suggested that grain weight exists in extensive genetic diversity duo to the genomic variations and various combinations of the grain weight-related to genes and QTL in rice.

Grain weight that is one of key factors determining grain yield, exists extensive genetic diversity in rice. As more and more grain weight related genes and QTLs will be cloned and characterized from genetic populations derived from indica and japonica hybrids or from wild and cultivated rice hybrids, which will build up fundamental regulation networks controlling grain weight and quality. Understanding the genetic and molecular mechanism of grain weight will contribute to pyramid positive alleles related to its determination using CRISPR gene editing as a precise tool in future molecular breeding.

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