Abstract
BackgroundCarbon (C) and nitrogen (N) are two fundamental components of starch and protein, which are important determinants of grain yield and quality. The food preferences of consumers and the expected end-use of grains in different rice-growing regions require diverse varieties that differ in terms of the grain N content (GNC) and grain C content (GCC) of milled rice. Thus, it is important that quantitative trait loci (QTLs)/genes with large effects on the variation of GNC and GCC are identified in breeding programs.ResultsTo dissect the genetic basis of the variation of GNC and GCC in rice, the Dumas combustion method was used to analyze 751 diverse accessions regarding the GNC, GCC, and C/N ratio of the milled grains. The GCC and GNC differed significantly among the rice subgroups, especially between Xian/Indica (XI) and Geng/Japonica (GJ). Interestingly, in the GJ subgroup, the GNC was significantly lower in modern varieties (MV) than in landraces (LAN). In the XI subgroup, the GCC was significantly higher in MV than in LAN. One, six, and nine QTLs, with 55 suggestively associated single nucleotide polymorphisms, were detected for the GNC, GCC, and C/N ratio in three panels during a single-locus genome-wide association study (GWAS). Three of these QTLs were also identified in a multi-locus GWAS. We screened 113 candidate genes in the 16 QTLs in gene-based haplotype analyses. Among these candidate genes, LOC_Os01g06240 at qNC-1.1, LOC_Os05g33300 at qCC-5.1, LOC_Os01g04360 at qCN-1.1, and LOC_Os05g43880 at qCN-5.2 may partially explain the significant differences between the LAN and MV. These candidate genes should be cloned and may be useful for molecular breeding to rapidly improve the GNC, GCC, and C/N ratio of rice.ConclusionsOur findings represent valuable information regarding the genetic basis of the GNC and GCC and may be relevant for enhancing the application of favorable haplotypes of candidate genes for the molecular breeding of new rice varieties with specific grain N and C contents.
Highlights
Carbon (C) and nitrogen (N) are two fundamental components of starch and protein, which are important determinants of grain yield and quality
Our findings represent valuable information regarding the genetic basis of the grain N content (GNC) and grain C content (GCC) and may be relevant for enhancing the application of favorable haplotypes of candidate genes for the molecular breeding of new rice varieties with specific grain N and C contents
A significant positive correlation between GNC and GCC was determined for the whole population (r = 0.30, P < 0.001), but the correlation was greater in XI (r = 0.33, P < 0.001) than in GJ (r = 0.22, P < 0.001), suggesting some differentiation in the GNC and GCC between the two rice subgroups (Additional file 2: Table S2)
Summary
Carbon (C) and nitrogen (N) are two fundamental components of starch and protein, which are important determinants of grain yield and quality. As a staple food for more than half of the global population, rice is one of the most widely grown cereals worldwide and is critical for food security. It is the source of about 25–50% of the daily protein intake. Increasing the grain N content (GNC), grain C content (GCC), and C/N ratio in milled rice is very important for improving the rice nutritional quality and yield. The economic development in Asia, with China as an example, has altered the rice breeding strategy from blindly pursuing higher yield to paying equal attention to high yield and quality as well as decreasing production costs, but maintaining safety (Tang et al 2017)
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