Abstract
Heterosis denotes the superiority of a hybrid plant over its parents. The use of heterosis has contributed significantly to yield improvement in crops. However, the genetic and molecular bases on heterosis are not fully understood. A large number of heterotic loci were identified for 12 yield-related traits in one parental population of chromosome segment substitution lines (CSSLs) and two test populations, which were interconnected by CSSLs derived from two rice genome-sequenced cultivars, Nipponbare and Zhenshan 97. Seventy-five heterotic loci were identified in both homozygous background of Zhenshan 97 and heterogeneous background of an elite hybrid cultivar Shanyou 63. Among the detected loci, at least 11 were colocalized in the same regions encompassing previously reported heterosis-associated genes. Furthermore, a heterotic locus Ghd8NIP for yield advantage was verified using transgenic experiments. Various allelic interaction at Ghd8 exhibited different heterosis levels in hetero-allelic combinations of five near-isogenic lines that contain a particular allele. The significant overdominance effects from some hetero-allelic combinations were found to improve yield heterosis in hybrid cultivars. Our findings support the role of allelic interaction at heterotic loci in the improvement of yield potential, which will be helpful for dissecting the genetic basis of heterosis and provide an optional strategy for the allele replacement in molecular breeding programs in hybrid rice.
Highlights
Heterosis or hybrid vigor refers to the phenomenon for which a hybrid markedly outperforms its parents
Most of the lines in the chromosome segment substitution lines (CSSLs) and BC populations had similar phenotypic performance as Zhenshan 97 (ZS97), except for several lines that showed significantly higher or lower values than ZS97 (Fig. 1; Additional file 1: Table S1), indicating that these lines carry either the introduced homozygous NIP or heterozygous NIP segments associated with the measured traits
Seventy-five heterotic loci (HLOS) were found co-localized in the same or overlapping regions of H LMP, indicating that both heterozygous NIP/ZS97 and NIP/Minghui 63 (MH63) alleles at the detected loci significantly affect heterosis in rice, the interaction effects were influenced by different genetic backgrounds
Summary
Heterosis or hybrid vigor refers to the phenomenon for which a hybrid markedly outperforms its parents. Xiong et al Rice (2021) 14:97 the identification of heterotic loci or genes support the significant role of the allelic interactions at both single locus and multiple loci in plant heterosis (Huang et al 2015; Li et al 2016; Liu et al 2020). In rice (Oryza sativa L.), Heading date 3a (Hd3a) has been identified to be responsible for heterosis in a large-scale F2 population (Huang et al 2016). The gene Ideal Plant Architecture (IPA1) that regulates plant architecture enhancing yield heterosis in rice, displays a strong overdominance effect from IPA1 heterozygotes (Huang et al 2016). The ortholog gene of IPA1 in maize (Zea mays L.), unbranched 3 (ub3) has been identified as the major candidate gene for heterosis advantage in three F2 populations (Liu et al 2020). Few cases where diverse effects of various allelic interactions at a heterotic locus have been reported
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