阿拉伯芥富亮胺酸重複類受體激酶 SRF6 參與熱反應之功能性研究

Abstract

富亮胺酸重複類受體激酶 (LRR-RLKs) 是植物細胞膜上最大的一群RLKs，但大部分成員之功能尚未知。為了探討RLKs基因在熱逆境反應 (HSR) 的角色，本研究檢測九個阿拉伯芥之RLK的突變株在熱逆境 (HS) 下之性狀，並且進一步分析一個受熱誘導表現的RLK基因STRUBBELIG-RECEPTOR-FAMILY 6 (SRF6) 的功能。SRF6 (At1g53730) 編碼一個LRR-RLK，經由先前的分析發現SRF6可能參與在HSR當中。SRF6為一個座落在細胞膜上的蛋白質，利用β-glucuronidase (GUS) 染色分析，發現SRF6廣泛分佈在植物體各時期的組織中。本篇利用細菌表現SRF6的激酶區段並進行活性分析，結果未顯示出其磷酸化活性。兩個不同程度減低SRF6表現量的T-DNA突變株在後天耐熱性 (SAT) 的檢測結果顯示，其存活率高於阿拉伯芥野生型，而大量表現SRF6的轉殖株之存活率則較低。另外，本篇在熱反應的表型觀察中發現，SRF6可能在植物熱逆境下的根生長恢復扮演重要的功能，且srf6植物之內質網 (ER) 逆境反應基因bZIP28和bZIP60的表現量顯著增加。本研究指出一個在植物根組織中非典型熱反應路徑的存在，且與SRF6以及ER逆境反應相關。

Leucine-Rich Repeat Receptor-like kinases (LRR-RLKs) comprise the largest family of plant RLKs, but most of them are still functionally unknown. To explore the role of RLKs in heat stress response (HSR), we characterized 9 RLK-mutant lines of Arabidopsis under HS condition and focused on functional analysis of a heat-responsive gene: STRUBBELIG-RECEPTOR- FAMILY 6 (SRF6). SRF6 (At1g53730) encodes a putative LRR-RLK and was suggested to play a role in the HSR pathway. Subcellular localization and tissue-specific expression analysis demonstrated that SRF6 is a membrane-bound protein and ubiquitously expressed in plants. This study concluded that the cytoplasmic kinase domain (CKD) of SRF6 is catalytically inactive. The srf6 mutants is less sensitive than wild type when challenged with a short-term acquired thermotolerance (SAT) test. Besides, analysis of the thermo-responsive root elongation phenotypes in srf6 highlighted that SRF6 plays a role in the control of root growth recovery from the HS. Analysis of the endodermis reticulum (ER)-stress-responsive genes showed that the expression levels of bZIP28 and bZIP60 were higher in srf6. The preliminary study indicates that the existence of a non-canonical HSR pathway involving SRF6 and ER-stress response in root growth.