Plant Physiology∣中國農業大學孫文獻課題組揭示水稻先天免疫機制

02-10

2017年12月14日Plant Physiology在線文章，該文章為中國農業大學孫文獻課題組完成，文章介紹了激酶OsCPK4的雙重功能，通過調控OsRLCK176的磷酸化狀態，OsCPK4可以調節OsRLCK176的穩定或是降解，從而實現對植物免疫的精細調節。

原題目為：

The kinase OsCPK4 regulates a buffering mechanism that fine-tunes innate immunity

摘要：

鈣依賴性蛋白激酶OsCPK4在水稻耐鹽，耐旱，植物生長和發育中發揮著重要作用。然而，在水稻免疫中，OsCPK4功能的分子機制知之甚少。在這項研究中，我們闡述了在oscpk4突變體中，由微生物相關分子模式（MAMPs）觸發的氧化爆發和致病相關基因的表達顯著增強。這些突變體比野生型植物更能抵抗細菌性枯萎病和真菌性疾病，表明OsCPK4負調控水稻的先天免疫。進一步鑒定了OsCPK4與類受體細胞質激酶OsRLCK176相互作用。 OsRKK176的積累受到OsCPK4的負調控。有意思的是，激酶失活的OsCPK4促進OsRLCK176的降解，並且表現出比正常的蛋白更強烈的降解。OsCPK4和OsRLCK176相互磷酸化並形成反饋迴路。此外，OsCPK4和OsRLCK176的激酶活性和磷酸化有助於OsRLCK176的穩定性。這些發現表明激酶失活的OsCPK4促進OsRLCK176降解並限制植物的防禦反應，而OsCPK4-OsRLCK176磷酸化的激活使OsRLCK176降解機制失效，從而增強植物免疫力。總之，本研究提出了一個由OsCPK4介導的新型防禦緩衝機制，可以精細的調節水稻中由MAMP觸發的免疫。

Abstract：

The calcium-dependent protein kinase OsCPK4 has been demonstrated to play important roles in salt and drought tolerance, plant growth and development in rice. However, little is known on molecular mechanisms underlying OsCPK4 function in rice immunity. In this study, we demonstrated that the generation of oxidative burst and pathogenesis-related gene expression triggered by microbe-associated molecular patterns (MAMPs) were significantly enhanced in the oscpk4 mutants. These mutant lines are more resistant to bacterial blight and fungal blast diseases than the wild-type plants, indicating that OsCPK4 negatively regulates innate immunity in rice. OsCPK4 was further identified to interact with a receptor-like cytoplasmic kinase OsRLCK176. OsRLCK176 accumulation is negatively regulated by OsCPK4. Interestingly, the kinase-dead OsCPK4 promotes OsRLCK176 degradation more strongly than the wild-type protein. OsCPK4 and OsRLCK176 mutually phosphorylate each other and form a feedback loop. Moreover, the kinase activity and phosphorylation of OsCPK4 and OsRLCK176 contribute to the stability of OsRLCK176. These findings indicate that the kinase-inactive OsCPK4 promotes OsRLCK176 degradation and restricts plant defenses; whereas the activation of OsCPK4-OsRLCK176 phosphorylation circuit invalidates the OsRLCK176 degradation machinery and thus enhancing plant immunity. Collectively, the study proposes a novel defense buffering mechanism mediated by OsCPK4, which fine-tunes MAMP-triggered immunity in rice.

圖7. OsCPK4在平衡水稻免疫中的工作模型

OsCPK4的非磷酸化形式處於休眠狀態，促進OsRLCK176降解，負調節水稻的植物免疫。這中降解最有可能是由泛素-蛋白酶體系統（UPS）介導的。在病原體攻擊和MAMP刺激後，OsCPK4和OsRLCK176相互磷酸化並形成反饋迴路，使得OsRLCK176更不易被降解，從而正調控水稻免疫力。在體內，OsRLKC176也可以被其他未知的激酶磷酸化。總之，依賴於其磷酸化狀態，OsCPK4可以調節OsRLCK176的降解和積累。

每日一詞
mutually

英[?mju:t?u?li]
美[?mju?t?u?li]
adv. 互相地，互助; 對;
[例句]She will try to arrange a mutually convenient time and place for an interview

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