西北農林科技大學在植物病原真菌蔗糖酶功能研究中取得新進展

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近日，西北農林科技大學康振生教授課題組在New Phytologist雜誌上在線發表了題為 「A unique invertase is important for sugar absorption of an obligate biotrophic pathogen during infection」的研究論文。該研究從小麥條鏽菌中鑒定獲得一個具有鏽菌特異性結構的蔗糖酶基因，通過分析該基因在小麥與小麥條鏽菌互作過程中的表達特徵與功能，闡明了病原真菌與植物互作過程中蔗糖酶水平升高的現象，並進一步揭示了植物病原真菌從寄主獲取糖類營養物質的機制。

Fig. Model depicting the effects of increased invertase activity

蔗糖是植物細胞中最主要的能源物質，然而活體營養專性病原真菌（如鏽菌、白粉菌）基因組上不存在蔗糖轉運蛋白基因，因此無法直接利用寄主蔗糖，而只能利用蔗糖的水解產物。大量研究表明，在植物受到病原物侵染組織中蔗糖酶活性會顯著升高，但是這一變化究竟由來自寄主蔗糖酶還是病原物蔗糖酶引起尚不明確，尤其是在活體營養寄生真菌與寄主互作過程中很難有效區分。儘管大量基因組測序工作表明在不同植物病原真菌中都存在蔗糖酶基因，但是它們在病原真菌侵染寄主植物過程中所起到的具體作用尚未得到證實。

該研究團隊以我國小麥生產上的重大病害—小麥條鏽病為研究對象，從小麥條鏽菌中克隆得到一個具有鏽菌特異性結構的蔗糖酶基因。通過對該基因的表達特徵分析發現該基因在小麥條鏽菌侵染小麥過程中大量表達並分泌到寄主中。同時該基因所編碼的蔗糖酶活性功能也在體內與體外系統得到了充分驗證，其所擁有的鏽菌特異性結構有利於病原菌與寄主競爭蔗糖。該研究首次在活體營養寄生真菌與寄主互作過程中通過HIGS技術對病原真菌的蔗糖酶功能進行了研究，結果表明該基因對於病原物的生長發育與繁殖都具有不可或缺的作用，也首次發現植物活體營養寄生真菌能通過自身產生並分泌蔗糖酶來分解寄主蔗糖以供應自身能量需要。

該研究由西北農林科技大學常青博士與劉傑教授為並列第一作者，西北農林科技大學康振生教授為通訊作者。相關工作得到了國家重點研發計劃、國家「973」計劃及高等學校學科創新引智計劃等項目的資助。

An increased invertase activity in infected plant tissue has been observed in many plant–pathogen interactions. However, the origin of this increased invertase activity (plant and/or pathogen) is still under debate. In addition, the role of pathogen invertases in the infection process is also unclear.We identified and cloned a gene with homology to invertases from Pucciniastriiformis f. sp. tritici(Pst). Transcript levels of PsINV were analyzed by quantitative reverse transcription PCR in both compatible and incompatible Pst–wheat interactions. Function of the gene product was confirmed by heterologous expression, and its function in Pst infection was analyzed by host-induced gene silencing (HIGS).Pst abundantly secretes invertase during its invasion attempts whether in a compatible or incompatible interaction with wheat. Further research into the different domains of this protein indicated that the rust-specific sequence contributes to a higher efficiency of sucrose hydrolysis. With PsINV silenced by HIGS during the infection process, growth of Pst is inhibited and conidial fructification incomplete. Finally, pathogenicity of Pst is impaired and spore yield significantly reduced.Our results clearly demonstrate that this Pstinvertase plays a pivotal role in this plant–pathogen interaction probably by boosting sucrose hydrolysis to secure the pathogen s sugar absorption.

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