ERF B1-a 基因群在植物青枯病與非生物逆境反應之功能研究

Abstract

各種生物性及非生物性逆境造成植物生長過程受限，而青枯病 (bacterial wilt) 是全球最嚴重的作物病害之一，但目前對於植物如何抵抗這類土壤傳播病害的防禦機制了解仍少。植物特有的乙烯反應轉錄因子 (ethylene-response factors, ERFs) 屬於 APETALA2 (AP2)/ethylene-responsive-element-binding protein (EREBP) 超級家族中的家族成員之一，在植物的逆境訊息傳遞反應中扮演重要角色。本研究針對番茄 ERF B1-a 基因群五個成員 (分別命名為 SlERF B1a-1,-2,-3,-4,-5) 在植物青枯病及缺水相關逆境反應之功能進行探討。本研究顯示番茄 ERF B1-a 蛋白群均位於細胞核內，皆具抑制轉錄活性的功能，但此五個基因的表現在植物不同組織及對青枯病菌感染、缺水逆境或植物防禦荷爾蒙處理有獨特性，且 VIGS 分析結果也顯示這些基因植物在防禦青枯病與乾旱逆境的反應上各有特殊影響。綜合SlERF B1a-1 的過量表現與短暫靜默之結果，推斷此基因在青枯病害與鹽害扮演正面角色，但在乾旱逆境扮演負面角色；然而，SlERF B1a-3 則在鹽害扮演正面角色，但在青枯病害與乾旱逆境扮演負面角色。此外，這兩個基因也參與乙烯/茉莉酸相關防禦途徑的調節。另一方面，SlERF B1a-1 在阿拉伯芥中之同源基因 At5g44210 的完全缺失突變株在鹽害、模擬乾旱、滲透壓、糖分及 ABA 之種子發芽率降低，但對青枯病、軟腐病及缺水逆境之反應則未有顯著改變。綜合目前結果顯示，五個 ERF B1a 基因可能對植物防禦反應及相關非生物逆境的耐受性各具獨特的功能。未來期望透過更深入探討 SlERF B1a 基因群在病害與非生物逆境之功能，建立 ERF B1a 基因群的抗逆境防禦機制與網絡。

Plants constantly encounter a wide range of abiotic and biotic stresses, leading to tremendous crop losses. Plant bacterial wilt (BW), a serious vascular disease caused by Ralstonia solanacearum (Rs), is one of the most complex and serious crop diseases worldwide. However, information on plant defense response to systemic soil-borne diseases is very limited. Ethylene-response factors (ERFs) are a subfamily of the APETALA2 (AP2)/ethylene-responsive-element-binding protein (EREBP) transcription factor superfamily and unique to plants. ERFs play a pivotal role in plant signaling transduction pathways switching extracellular signals into cellular responses. In this study, roles of five uncharacterized members of tomato ERF cluster B1-a, namely SlERF B1a-1,-2,-3,-4,-5, in plant response to BW and water deficit (WD) are investigated. These ERFs localize in nucleus and confer transcriptional repression activity. These genes display differential transcriptional expression patterns in various tissues and under, treatments of Rs, drought and defense phytohormones, implying they may have distinct functions. VIGS assays further revealed their differential roles in tomato defense to BW and water deficit (WD) response. Results of functional analyses by VIGS and transgenic overexpression suggest that SlERF B1a-1 may play a positive role in defense to BW and salinity, and a negative role in drought. However, SlERF B1a-3 may play a negative role in defense response to BW and drought, and a positive role in salinity. Furthermore, functioning of these two genes involves ET/JA (ethylene/ jasmonic acid)-related pathways. On the other hand, reduced seed germination rates of Arabidopsis at5g44210 null mutants, an othorlogous gene of SlERF B1a-1, indicated a function of this gene in various abiotic stresses. However, mature plants of the null mutants displayed unaltered response to Rs, Pectobacterium chrysanthemi and drought treatments. Together, these results demonstrate important overlapping and differential roles of the studied ERF cluster B1-a members in plant response to biotic and abiotic stresses. These studies, along with further suggested analyses, are expected to decipher multiple functions of these proteins and to establish the related regulatory networks in plant stress responses.