凝集素受體激酶LecRK-V.5與引朵基丁酸反應基因3參與在病原相關分子模式引發的免疫反應在阿拉伯芥中

Abstract

植物氣孔可以限制病原菌進入葉子中，因此在植物的第一道免疫防禦反應中扮演著重要的角色。但是當接觸到病原菌後，調控氣孔開關的機制還不甚清楚。在這裡我們發現了在阿拉伯芥中的凝集素受體激酶LecRK-V.5扮演著一個負向調控氣孔免疫的角色。當LecRK-V.5失去功能，並利用表面感染法感染細菌性斑點病原菌Pseudomonas syringae pv tomato DC3000之後，植物會增加對此並原菌的抵抗力。但是當我們用注射法感染植物，失去LecRK-V.5功能的植物感染力與野生型植物並無太大差異。這暗示著LecRK-V.5可作用在植物的早期防禦。過度表現LecRK-V.5會使植物對Pst DC3000較敏感，這個現象也可歸咎於過度表現LecRK-V.5會使氣孔在處理Pst DC3000之後有較早恢復開關的現象。此外，過度表現LecRK-V.5在處理病源相關分子模式Pathogen-associated molecular patterns (PAMPs)以及H2O2之後喪失了氣孔開關的能力。這些結果提供了一個LecRK-V.5可負向調控在ROS合成上游的氣孔免疫在基因層次上的證據，也顯示了凝集素受體激酶家族在氣孔調節上的一個新功能。 引朵基丁酸反應基因3(IBR3)長久以來被認為的功能是一個參予在引朵基丁酸轉換成引朵基乙酸之間的一個酵素。在這裡我們證實了IBR3可能也在植物免疫防禦反應中扮演著一個角色。過度表現IBR3使得植物對於Pst DC3000有較高的敏感性，也有植物防禦反應降低的情形。此外，在處理Pst DC3000分泌系統3缺失的Pst DC3000 hrcC－以及PAMPs之後，降低植物PAMPs誘發免疫反應也發生在過度表現IBR3的植物中。這些結果提供了IBR3參予在植物PAMPs誘發免疫反應的一個新角色。

Stomata play an important role in plant innate immunity by regulating stomatal closure upon pathogen attack, but the mechanisms regulating stomatal closure are not well understood. Here we show that the Arabidopsis thaliana L-type lectin receptor kinase-V.5 (LecRK-V.5) negatively regulates stomatal closure. Previously in our lab, loss of LecRK-V.5 function was shown to increase resistance to surface inoculation with virulent bacteria Pseudomonas syringae pv tomato DC3000, but not to infiltration-inoculation, suggesting that LecRK-V.5 functions at an early defense stage. To further evaluate a possible involvement of LecRK-V.5 in Arabidopsis disease resistance, a gain-of-function approach was used. Overexpression of LecRK-V.5 was associated with early stomatal reopening after Pst DC3000 treatment and a defective stomatal closure after PAMPs treatment could be correlated with sensibility to Pst DC3000. Stomata of lines overexpressing LecRK-V.5 had normal response to MeJA and SA, but were insensitive to ABA. However, stomata of lines overexpressing LecRK-V.5 showed normal response to H2O2. These results provide genetic evidences that LecRK-V.5 negatively regulates ABA-mediated stomatal closure upstream of ROS synthesis, revealing a novel receptor-like kinase family with a function in stomatal movement. IBR3 gene is known the function in the conversion of IBA to IAA. Here we show that IBR3 may also play a role in plant defense responses. Lines overexpressing IBR3 demonstrated increased susceptibility to Pst DC3000 and a weaker activation of defense responses upon Pst DC3000 infection. The increased susceptibility phenotype of IBR3 overexpressors to Pst DC3000 could indeed be correlated with a defective SA defense signaling and impairment in pattern-triggered immunity (PTI) activation. Notably, PTI-mediated callose deposition and ROS production, and accumulation of the PTI-responsive transcript FRK1 were delayed in lines overexpressing IBR3. These results suggest a new function for IBR3 in plant defense response against bacterial pathogens.