The kinase OsSK41/OsGSK5 negatively regulates amylose content in rice endosperm by affecting the interaction between OsEBP89 and OsBP5

Zejun Hu, Fuan Niu, Peiwen Yan, Kai Wang, Lixia Zhang, Ying Yan, Yu Zhu, Shiqing Dong, Fuying Ma, Dengyong Lan, Siwen Liu, Xiaoyun Xin, Ying Wang, Jinshui Yang, Liming Cao, Shujun Wu, Xiaojin Luo

Journal of Integrative Plant Biology, 2023, 65(7): 1782-1793  DOI: 10.1111/jipb.13488;      追溯原文......本站官方QQ群：62473826

AP2/EREBP transcription factor; endosperm amylose content; GSK3‐like family protein; MYC‐like protein; OsSK41/OsGSK5; OsEBP89; OsBP5; rice grain

1. 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
2. State Key Laboratory of Genetic Engineering and MOE Engineering Research Center of Gene Technology, School of Life Sciences, Fudan University, Shanghai 200438, China
3. MOE Key Laboratory of Crop Physiology, Ecology and Genetic Breeding College of Agronomy, Jiangxi Agricultural University, Nanchang 330045, China

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^E–OsBP5 but relatively strong when regulated by the nonphosphorylatable variant OsEBP89^A–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.

激酶OsSK41/OsGSK5通過影響OsEBP89和OsBP5之間的相互作用，負調(diào)控水稻胚乳中的直鏈淀粉含量

直鏈淀粉含量(AC)是決定稻米適口性、粘度、透明度和消化率的主要因素。水稻籽粒中的AC主要由Waxy(Wx)及其相關(guān)的基因控制。植物糖原合成酶激酶(GSKs)能磷酸化底物蛋白質(zhì)以調(diào)節(jié)其活性、亞細胞定位和穩(wěn)定性，是各種信號通路的重要調(diào)節(jié)因子，在控制水稻籽粒發(fā)育的過程中發(fā)揮著重要作用。然而，目前對植物糖原合成酶激酶介導(dǎo)的磷酸化是否參與水稻籽粒直鏈淀粉合成及其調(diào)控的分子機制尚不清楚。該研究發(fā)現(xiàn)水稻糖原合成酶激酶OsSK41/OsGSK5能夠通過磷酸化OsEBP89負調(diào)控水稻籽粒直鏈淀粉的合成。
  羅小金課題組在前期研究中發(fā)現(xiàn)一個與水稻籽粒大小相關(guān)的主效QTL：qTGW3 (LOC_Os03g62500)，它編碼一個截短的GSK3/SHAGGY-like蛋白激酶 (OsGSK5/OsSK41)，能夠顯著增加水稻籽粒的長度和千粒重。在此基礎(chǔ)上，研究人員測量了qTGW3/OsSK41近等基因系(NIL-tgw3和NIL-TGW3)稻米的蒸煮、食味和營養(yǎng)品質(zhì)，發(fā)現(xiàn)OsSK41對水稻籽粒的AC具有負調(diào)控作用。在粳稻日本晴背景下，敲除該基因的突變體其稻米AC增加，并且Wx基因的表達水平也顯著提高。OsSK41與Wx表達調(diào)控相關(guān)的轉(zhuǎn)錄因子OsEBP89在細胞核中互作，并磷酸化其四個位點的氨基酸 (Thr-28，Thr-30，Ser-238和Thr-257)。OsSK41介導(dǎo)的磷酸化，使OsEBP89變得不穩(wěn)定，并減弱它與OsBP5的互作，從而抑制了它們對Wx基因的協(xié)同激活作用。因此，該研究揭示了水稻籽粒發(fā)育過程中直鏈淀粉合成的新層次分子調(diào)控機制，并為通過精準基因編輯調(diào)節(jié)水稻籽粒AC提供了新思路。

►基因列表◄
  與光敏色素互作的類bHLH因子; PIL轉(zhuǎn)錄因子 OsPIL12; OsBP-5; OsBP5
  EREBP轉(zhuǎn)錄因子 OsEBP89
  GSK3/SHAGGY樣激酶; 籽粒大小; 千粒重; 粒長 qTGW3; qGL6; OsSK41; OsGSK5; qGL3.3