基于碳代谢解析大穗型粳稻弱势粒灌浆启动的机制

Inferior spikelets (IS) of large-panicle rice have obvious “diapause period” after fertilization, which leads to later and poorer filling of IS, and seriously restricts the improvement of rice yield and quality. However, the transition mechanism of the IS from diapause to filling stage is still partially understood. Our previous work found that non-structural carbohydrate (NSC) reserved in the stem and sheath before heading significantly affected IS filling. In this study, two large-panicle japonica rice varieties with significant difference in grain filling between superior spikelets (SS) and IS will be selected as the materials, and the content of NSC reserved in the stem and sheath at heading will be changed through the shading and single stem removing treatments, so as to establish the rice population with different IS filling initiation. Beginning from the spikelets fertilization, to study the effects of NSC reserved in the stem and sheath on the carbon metabolism physiology of IS during diapause and filling stage, so as to understand the physiological mechanism of NSC regularization on the IS filling initiation. Based on RNA-Seq transcriptomics technology to screen key genes that restricted the initiation of IS filling. RNAi technology was used to explore differentially expressed gene during the transition from diapause to filling stage, then through functional verification of candidate genes as well as their temporal and spatial expression analysis, to reveal the molecular mechanism for the stagnation / initiation of IS filling in rice. The above studies will help to reveal the causes of poor IS filling in depth, and provide the theoretical basis for the genetic improvement and cultivation regulation of large-panicle japonica rice.

大穗型水稻弱势粒在受精后存在明显的“滞育期”，导致弱势粒灌浆启动迟、充实差，严重制约了水稻产量和品质的提升。目前，关于水稻弱势粒从滞育期到灌浆期转换的机制尚不明确。申请者前期研究发现，水稻抽穗期茎鞘非结构性碳水化合物（NSC）显著影响弱势粒的灌浆充实。本研究拟选用强、弱势粒灌浆差异显著的两个大穗型粳稻品系，通过遮荫和疏单茎处理，改变抽穗期茎鞘NSC贮存量，构建弱势粒灌浆启动差异的水稻群体。从籽粒受精后开始，深入研究茎鞘NSC对滞育期及灌浆期籽粒碳代谢生理的影响，明确茎鞘NSC调控弱势粒灌浆启动的碳代谢生理机制；利用RNA-Seq转录组学技术，筛选限制弱势粒灌浆启动的关键基因，再运用RNA干扰和基因过表达技术，对候选基因进行功能验证与表达模式分析，揭示水稻弱势粒灌浆停滞及启动的分子机制。该研究将有助于深入揭示弱势粒灌浆不良的形成原因，同时为大穗型粳稻的遗传改良及其栽培调控提供理论依据。

大穗型水稻弱势粒在受精后存在明显的“滞育期”，导致弱势粒灌浆启动迟、充实差，严重制约了水稻产量和品质的提升。目前，关于水稻弱势粒从滞育期到灌浆期转换的机制尚不明确。申请者前期研究发现，水稻抽穗期茎鞘非结构性碳水化合物（NSC）显著影响弱势粒的灌浆充实。本研究选用强、弱势粒灌浆差异显著的两个大穗型粳稻品系，通过遮荫和疏单茎处理，改变抽穗期茎鞘NSC贮存量，构建弱势粒灌浆启动差异的水稻群体。研究结果表明遮荫和疏蘖处理可改变水稻抽穗期茎鞘NSC的贮存量，且发现抽穗期的糖花比显著影响弱势粒的灌浆结实性，进一步发现抽穗前糖花比与弱势粒的结实率与粒重之间均存在Y=(a+bx)/x的曲线相关关系。在水稻弱势粒灌浆启动过程中，主要进行蔗糖分解与淀粉合成活动，处于灌浆启动期籽粒具有较低的可溶性碳水化合物含量及较高的淀粉含量，且发现在此过程中起主要作用的酶为SuSase, AGPase和SBE。同时，还发现弱势粒灌浆启动是个耗能过程，需要消耗大量的ATP。水稻弱势粒灌浆启动还受内源植物激素的调节，研究发现在弱势粒灌浆启动过程中起主要作用的激素为IAA及CTK。还发现MJ及SA在此过程中也有重要作用。同时，筛选出了碳代谢关键基因：SuS3, AGPL2, GBSSII, SBEI, SBEⅡb, SBEⅢ。研究还发现糖花比与弱势粒的稻米加工品质和直链淀粉含量呈显著正相关性，与垩白粒率、垩白度和蛋白质呈显著负相关。增加抽穗期的糖花比可改善稻米的品质。该研究有助于深入揭示弱势粒灌浆不良的形成原因，同时为大穗型粳稻的遗传改良及其栽培调控提供理论依据。.