Heterosis analysis of neo-tetraploid rice line

Neo-tetraploid rice, which is a new germplasm developed from autotetraploid rice, has a powerful biological and yield potential and could be new rice for commercial utilization. In the present study, we developed a neo-tetraploid rice line, Huaduo 8, with long panicles and harboring wide-compatibility genes for pollen and embryo sac fertility. All the hybrids generated by crossing with Huaduo 8 produced significant high-parent yield heterosis and displayed long panicles similar to Huaduo 8. RNA-seq analysis detected a total of 4013, 7050, 6787 and 6195 differentially expressed genes uniquely belonging to F1 and specifically (DEGFu-sp) associated with leaf, sheath, main panicle axis and spikelet in the two hybrids, respectively. Of these DEGFu-sp, 1371 common DEGFu-sp were detected in the two hybrids, in which 80 and 29 genes were involved in kinase and synthase, respectively. Moreover, 92 known QTLs associated with heterosis, such as sd1, OsGA20ox2, qSD1-2, Hd3a and FT, were also identified. Importantly, 9 up-regulated genes associated with panicle flower were detected in young panicles of the two hybrids compared to their parents, including Gn1a, OsClpC2, OsLG1, MULTI-FLORET SPIKELET1, and so on. Re-sequencing analysis depicted that DNA variations in LP (a genes controlling long panicle) of H8 was different from many other neo-tetraploid rice lines and most of autotetraploid and diploid rice. The qRT-PCR results showed that LP was up-regulated in the hybrid compared to its parents at very young stage of panicle development. These results suggested that the neo-tetraploid rice is a useful germplasm for polyploid rice breeding, and provided insight into complex molecular mechanisms associated with heterosis in neo-tetraploid rice.