Unique Transcriptome And Gene Expression Analysis of Flag Leaves of A Super-Hybrid Rice WFYT025

Background: The health and physiology of flag leaves are closely related to rice yield, and flag leaves play an important role in providing photosynthetic products during grain filling, many breeding studies have tried to improve the performance of flag leaves. However, there are few studies on the heterosis of rice flag leaves up to now. Results: Thus, the present research is focused on the flag leaves heterosis of a widely used late-cropping indica super hybrid rice combination WFYT025 in China using a high-throughput next-generation RNA-seq strategy under different environment with two stages, trying to find some genes related to photosynthesis, transpiration, and development of seeds. Mid-parent heterosis (MPH) and higher parent heterosis (HPH) were estimated for the heterosis of flag leaf. Under the environment of middle rice, the number of genes up-regulated in CHT025, WFB and WFYT025 were 892,1,273 and 819, down-regulated in CHT025, WFB and WFYT025 were 616,1934 and 2196, respectively. Among the SDGhps on the first day after flowering, 10.9% had a dominant effect, 41.81% had a partial dominant effect, 22.07% had an additive effect and the remaining 25.22% had an over-dominant effect. Meanwhile, on the tenth day after flowering, there were 491 genes, accounting for 27.16%, showed over-dominance; 222 genes, accounting for 12.28%, showed dominance; 760 genes, accounting for 42.04%, showed partial dominance; and 335 genes, accounting for 18.52%, showed additive effect. Conclusion: The co-expressed gene sets via weighted gene co-expression network analysis (WGCNA) were identified, and total of 5,000 highly expressed genes were divided into 24 co-expression groups. In the two stages, we found 9 identical transcription factors. Except for 5 reported TFs, the other 4 TFs may play an important role in grain number and photosynthesis heterosis.

Plant–atmosphere and soil–atmosphere temperature differences and their impact on grain yield of super hybrid rice under different irrigation conditions

Continued drought during the late growth stage of super hybrid rice (SHR) markedly reduces yield, and management practices that use water more efficiently can contribute greatly to high and stable yields from SHR. The absolute temperature differences (ATDs) between the rice plant and the atmosphere and between the soil and the atmosphere are believed to be important determinants of grain yield. However, it has not previously been determined whether these ATDs have any effect on SHR yields under water-saving cultivation. A two-year field experiment involving two SHR varieties, Liangyoupeijiu (LYPJ) and Y-Liangyou 9000 (YLY900), evaluated the effects of reducing water supply from mid-booting to maturity on grain yield, canopy relative humidity (CRH), leaf area index (LAI), and ATDs between the ambient temperature and the leaf surface, panicles, canopy, and soil. Grain yield increased significantly under shallow water irrigation (SW), by 8.84% (YLY900) and 12.26% (LYPJ), but decreased significantly under mild water stress (MS, −20 to −30 kPa), by 14.36% (YLY900) and 9.47% (LYPJ), as well as severe water stress (SS, −40 to −50 kPa), by 35.06% (YLY900) and 28.74% (LYPJ). As water supply decreased, so did the CRH and the ATDs, with significant decreases under MS and SS. The temperature differences were significantly and positively correlated with grain yield (P < 0.01) in both cultivars. LAI was increased under SW conditions, but was significantly decreased under MS and SS. Our study suggests that the dual goal of saving water while maintaining high yield can be achieved by applying SW irrigation from mid-booting to maturity and by adopting cultivation measures that maintain high CRH and high plant–atmosphere and soil–atmosphere ATDs in order to alleviate water stress. YLY900 has a higher yield potential than LYPJ under SW conditions, suggesting that its wide cultivation may help achieve this dual goal.

Higher Radiation Use Efficiency Produces Greater Biomass Before Heading and Grain Yield in Super Hybrid Rice

To reveal the physiological mechanism underlying the yield advantage of super hybrid rice compared with inbred super rice, a super hybrid rice cultivar Yliangyou 3218 (YLY) and an inbred super rice cultivar Zhendao 11 (ZD) were field grown under five nitrogen (N) fertilizer rates in 2016 and 2017. The average grain yield of YLY across nitrogen fertilizer rates was 10.1 t ha−1 in 2016 and 9.7 t ha−1 in 2017, 29.6% and 21.3% higher than that of ZD in 2016 and 2017, respectively. YLY showed higher above-ground biomass accumulation, especially growth before heading, which was mainly due to its faster green leaf area index (GLAI) formation and greater maximum GLAI (GLAImax). The daily radiation interception (RIdaily) was 15.0% higher in YLY than ZD, but the accumulated radiation interception (RIacc) before heading showed little difference between them because ZD had a longer growth duration. The radiation use efficiency (RUE) of YLY before heading was 54.7% higher than that of ZD (YLY, 2.12 g MJ−1; ZD, 1.37 g MJ−1). Our result demonstrated that the yield advantage of YLY was due to its higher above-ground biomass before heading, which was mainly achieved by its improvement in RUE rather than radiation interception.