Key Laboratory of Germplasm Innovation and Genetic Improvement of Grain and Oil Crops (Co-construction by Ministry and Province), Ministry of Agriculture and Rural Affairs, Crop Breeding and Cultivation Research Institute, Shanghai Academy of Agricultural Sciences, Shanghai, 201403, China.
State Key Laboratory of Genetic Engineering and MOE Engineering Research Center of Gene Technology, School of Life Sciences, Fudan University, Shanghai, 200438, China.
J Integr Plant Biol. 2023 Jul;65(7):1782-1793. doi: 10.1111/jipb.13488. Epub 2023 Apr 21.
Amylose content (AC) is the main factor determining the palatability, viscosity, transparency, and digestibility of rice (Oryza sativa) grains. AC in rice grains is mainly controlled by different alleles of the Waxy (Wx) gene. The AP2/EREBP transcription factor OsEBP89 interacts with the MYC-like protein OsBP5 to synergistically regulate the expression of Wx. Here, we determined that the GLYCOGEN SYNTHASE KINASE 5 (OsGSK5, also named SHAGGY-like kinase 41 [OsSK41]) inhibits the transcriptional activation activity of OsEBP89 in rice grains during amylose biosynthesis. The loss of OsSK41 function enhanced Wx expression and increased AC in rice grains. By contrast, the loss of function of OsEBP89 reduced Wx expression and decreased AC in rice grains. OsSK41 interacts with OsEBP89 and phosphorylates four of its sites (Thr-28, Thr-30, Ser-238, and Thr-257), which makes OsEBP89 unstable and attenuates its interaction with OsBP5. Wx promoter activity was relatively weak when regulated by the phosphomimic variant OsEBP89 -OsBP5 but relatively strong when regulated by the nonphosphorylatable variant OsEBP89 -OsBP5. Therefore, OsSK41-mediated phosphorylation of OsEBP89 represents an additional layer of complexity in the regulation of amylose biosynthesis during rice grain development. In addition, our findings provide four possible sites for regulating rice grain AC via precise gene editing.
直链淀粉含量（AC）是决定稻米（Oryza sativa）口感、黏度、透明度和消化率的主要因素。稻米粒中的 AC 主要由 Waxy（Wx）基因的不同等位基因控制。AP2/EREBP 转录因子 OsEBP89 与 MYC 样蛋白 OsBP5 相互作用，协同调控 Wx 的表达。在这里，我们确定糖原合成激酶 5（OsGSK5，也称为 SHAGGY-like kinase 41 [OsSK41]）在直链淀粉生物合成过程中抑制水稻粒中 OsEBP89 的转录激活活性。OsSK41 功能丧失增强了 Wx 的表达，增加了稻米粒中的 AC。相比之下，OsEBP89 功能丧失降低了 Wx 的表达，降低了稻米粒中的 AC。OsSK41 与 OsEBP89 相互作用，并磷酸化其四个位点（Thr-28、Thr-30、Ser-238 和 Thr-257），这使得 OsEBP89 不稳定，并减弱其与 OsBP5 的相互作用。当受磷酸模拟变体 OsEBP89-OsBP5 调控时，Wx 启动子活性相对较弱，而当受非磷酸化变体 OsEBP89-OsBP5 调控时，Wx 启动子活性相对较强。因此，OsSK41 介导的 OsEBP89 磷酸化代表了在水稻籽粒发育过程中直链淀粉生物合成调控的另一个复杂性层次。此外，我们的研究结果为通过精确的基因编辑调控稻米粒 AC 提供了四个可能的位点。
