阿拉伯芥凝集素受體激酶6.2參與植物對抗細菌誘發之基本性免疫作用

Abstract

藉由感知病原菌特定分子標誌(pathogen-associated molecular patterns, PAMPs)，植物可感應病原菌的入侵，進而引發植物中的PAMP誘導免疫反應(PAMP-triggered immunity, PTI)。 本論文發現，阿拉伯芥之凝集素受體激酶6.2(Lectin receptor kinase -VI.2, LecRK-VI.2)，在植物抗病反應中，扮演正面的調控角色。LecRK-VI.2的T-DNA插入突變株，lecrk-VI.2-1，對於半活體寄生型(hemi-biotrophic)的細菌性斑點病病原菌(Pseudomonas syringae pv tomato DC3000)與死體寄生型(necrotrophic)的細菌性軟腐病病原菌(Erwinia carotovora subsp. carotovora)較為感病，顯示LecRK-VI.2可能參與植物抗病之防禦反應。 我們的分析資料顯示，lecrk-VI.2-1在被細菌感染或經細菌PAMPs處理後，其PTI標的基因(例如FRK1和WRKY29)的轉錄活性有缺陷，但對於細菌PAMP幾丁質的反應則不受影響。同時，經細菌或細菌PAMPs處理後，lecrk-VI.2-1之胝質蓄積(callose deposition)量較少，其氣孔關閉反應也有缺陷，顯示LecRK6.2的突變會導致多方面PAMP誘導免疫反應的缺失。 於互補實驗中，在突變株的背景下表現LecRK-VI.2，可以回復PTI標的基因的轉錄活性、胼質醣合成及氣孔關閉反應，也可以回復此植株對於細菌性入侵的抗病性。 此外，本論文發現，LecRK-VI.2大量表現的轉殖株會持續性的表現PAMP誘導免疫反應，包括擁有高基礎轉錄活性(basal transcriptional level)的PTI標的基因表現、持續性的胝質蓄積及關閉的氣孔。這些持續性的PAMP誘導免疫反應使轉殖株對於細菌性病原菌斑點病病原菌和軟腐病病原菌之抗病性提升，但對於卵菌性黃葉病病原菌的抗病性卻與野生株Col-0相似。 由以上結果，可以推論LecRK-VI.2對於細菌引發的PAMP誘導免疫反應，扮演一個正向的調節因子。

Plants can sense pathogen infections through perception of pathogen-associated molecular patterns (PAMPs) by pattern-recognition receptors (PRRs) located on the cell surface. Recognition leads to enhanced plant resistance through the activation of PAMP-triggered immunity (PTI). Here we report that the LECTIN RECEPTOR KINASE-VI.2 (LecRK-VI.2) is essential for Arabidopsis PTI. lecrk-VI.2-1, a LecRK-VI.2 knock-out mutant, was less resistant to the hemi-biotrophic bacterial pathogen Pseudomonas syringae pv tomato (Pst) DC3000 and the necrotrophic bacterial pathogen Erwinia carotovora subsp. carotovora (Ecc) bacteria, suggesting LecRK-VI.2 is required for efficient plant defense response. lecrk-VI.2-1 was deficient in the transcriptional activation of PTI marker genes such as FRK1 and WRKY29 upon inoculation with bacteria and various bacterial PAMPs such as flg22, efl-26 and peptidoglycan (PGN). However, lecrk-VI.2-1 demonstrated a normal response to the fungal PAMP chitin. lecrk-VI.2-1 was also impaired in callose deposition and stomatal response, two typical PTI responses, when challenged with Pst DC3000 and bacterial PAMPs. Together my results suggest that LecRK-VI.2 is involved in the PTI response triggered by the perceptions of bacterial PAMPs but not the fungal chitin PAMP. Over-expression of LecRK-VI.2 in lecrk-VI.2-1 background restored resistance to bacterial microbes and PTI responses to a wild-type level. In addition, high-levels of LecRK-VI.2 expressions in lecrk-VI.2-1 background constitutively activated PTI responses. Such transgenics were found to be highly resistant to bacteria, but confer normal response to the fungal pathogen Botyris cinerea. Our data suggest that LecRK-VI.2 acts as a positive regulator of the Arabidosps PTI by participating in defense mechanisms such as PTI gene activations, callose deposition and stomatal responses.