To understand the molecular basis of environment-induced and genotype-dependent chalkiness, six rice genotypes showing variable chalk levels were subjected to gene expression analysis during reproductive stages. In the high chalk genotypes, the peak expressions of ADP-Glucose Pyrophosphorylase (AGPase) Large Subunit 4 (AGPL4) occurred in the stages before grain filling commenced, creating a temporal gap with the upregulation of Granule Bound Starch Synthase I (GBSSI) and Starch Synthase IIA (SSIIA). Whereas, in the low chalk genotypes, AGPL4 expression generally occurred in later stages, close to the upregulation of GBSSI and SSIIA. However, heat treatment altered the expression pattern and created a gap between the expression peaks of AGPL4, and GBSS1 and SSIIA. This change was accompanied by transformed granular morphology, increased protein content, and chalkiness in the grains. AGPL4 expression pattern may partially explain chalkiness as it contributes to the pool of ADP-Glucose for producing amylose and amylopectin, the major components of the starch. Down-regulation of AGPase during grain filling stages could result in a limited pool of ADP-Glucose leading to inefficient grain filling and air pockets that contribute to chalkiness. The study suggests a mechanism of grain chalkiness based on the coordination of the three starch biosynthesis genes in rice.

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水稻基因型依赖性和热诱导的垩白度与淀粉生物合成基因的表达模式相关

为了了解环境诱导的和基因型依赖性白垩化的分子基础，在繁殖期对六种显示不同白垩水平的水稻基因型进行了基因表达分析。在高白垩基因型中，ADP-葡萄糖焦磷酸化酶（AGPase）大亚基4（AGPL4）的高峰表达发生在籽粒灌浆开始之前的阶段，随着颗粒结合淀粉合酶I（GBSSI）和淀粉的上调产生了暂时的缺口。合酶IIA（SSIIA）。而在低白垩基因型中，AGPL4表达通常发生在后期，接近GBSSI和SSIIA的上调。但是，热处理改变了表达模式，并在AGPL4，GBSS1和SSIIA的表达峰之间产生了间隙。这种变化伴随着颗粒形态的转变，增加蛋白质含量和谷物中的白垩度。AGPL4表达模式可以部分解释白垩化，因为它有助于产生淀粉的主要成分直链淀粉和支链淀粉的ADP-葡萄糖库。谷物填充阶段AGPase的下调可能会导致ADP葡萄糖池数量有限，从而导致谷物填充效率低下和产生白垩度的气穴。该研究提出了基于水稻中三个淀粉生物合成基因的协调的谷物垩白的机制。谷物填充阶段AGPase的下调可能会导致ADP葡萄糖池数量有限，从而导致谷物填充效率低下和产生白垩度的气穴。该研究提出了基于水稻中三个淀粉生物合成基因的协调的谷物垩白的机制。谷物填充阶段AGPase的下调可能会导致ADP葡萄糖池数量有限，从而导致谷物填充效率低下和产生白垩度的气穴。该研究提出了基于水稻中三个淀粉生物合成基因的协调的谷物垩白的机制。