Integrated analysis of phenome, genome, and transcriptome of hybrid rice uncovered multiple heterosis-related loci for yield increase

Significance Because of its practical importance and scientific significance, heterosis (hybrid vigor) is an interesting topic for both breeders and biologists. However, although heterosis has been applied successfully to increase crop yields, the molecular mechanisms involved remain obscure. In this study, using an integrative approach, we found that multiple quantitative trait loci (QTLs) cumulatively drive yield heterosis in hybrid rice by regulating two grain-yield component traits in which the RH8 (rice heterosis 8) gene plays a major role. Our research highlights the importance of integrative methods to uncover the molecular mechanism of heterosis and thus pave a way toward revealing the molecular mechanisms in rice heterosis in detail. Hybrid rice is the dominant form of rice planted in China, and its use has extended worldwide since the 1970s. It offers great yield advantages and has contributed greatly to the world’s food security. However, the molecular mechanisms underlying heterosis have remained a mystery. In this study we integrated genetics and omics analyses to determine the candidate genes for yield heterosis in a model two-line rice hybrid system, Liang-you-pei 9 (LYP9) and its parents. Phenomics study revealed that the better parent heterosis (BPH) of yield in hybrid is not ascribed to BPH of all the yield components but is specific to the BPH of spikelet number per panicle (SPP) and paternal parent heterosis (PPH) of effective panicle number (EPN). Genetic analyses then identified multiple quantitative trait loci (QTLs) for these two components. Moreover, a number of differentially expressed genes and alleles in the hybrid were mapped by transcriptome profiling to the QTL regions as possible candidate genes. In parallel, a major QTL for yield heterosis, rice heterosis 8 (RH8), was found to be the DTH8/Ghd8/LHD1 gene. Based on the shared allelic heterozygosity of RH8 in many hybrid rice cultivars, a common mechanism for yield heterosis in the present commercial hybrid rice is proposed.

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