Transcriptional regulation of Arabidopsis phloem-defenses as a paradigm to explore molecular mechinisam underlying wheat resistance to aphids | 拟南芥韧皮部防卫反应转录调控与小麦抗蚜虫机制

chinois. 植物在受蚜虫侵袭时,乙烯或茉莉酸信号与MYB转录因子调控韧皮部防卫反应,凝集素类韧皮部蛋白（PP）与葡聚糖合酶（GSL）催化生成的胼胝质堵塞筛管细胞壁和筛孔,妨碍蚜虫刺吸韧皮部。根据笔者在拟南芥上的研究,韧皮部防卫反应由转录因子AtMYB44与乙烯信号调控,AtMYB44直接作用于乙烯信号传导调控因子EIN2,启动EIN2基因表达,EIN2转而调控韧皮部防卫反应和对桃蚜的抗性。与拟南芥相比,普通小麦基因组容量超出120多倍,不同基因家族成员冗余程度很高,功能复杂,多种机制交叉作用,影响抗虫防卫反应。小麦编码MYB、GSL和凝集素及其受体蛋白的73、22和50种基因已有全长序列克隆,哪些基因参与小麦针对蚜虫的韧皮部防卫反应以及它们与乙烯或茉莉酸信号的功能关系等问题,目前还不清楚。通过信号传导抑制剂药理学试验与基因沉默效应,鉴定参与小麦抗蚜作用的乙烯或茉莉酸信号传导因子;使用基因沉默、过表达以及荧光蛋白激光共聚焦检测技术,鉴定受乙烯或茉莉酸调控并对小麦抗蚜有调控功能的MYB、PP和GSL种类;通过染色质免疫沉淀等试验,研究MYB对PP和GSL基因表达直接或间接的调控作用,可以阐释小麦抗蚜防卫反应转录调控与信号传导的关键环节。

anglais. Phloem-feeding insects are highly speciahzed in their mode of feeding and present a unique stress on plant fitness. These insects use their slender stylets to feed from a single-cell type, the phloem sieve element. In response, plants defend themselves by using the phloem-based defense （PBD）. A suggested PBD component is the lectin-type phloem protein （PP）, which may form high molecular weight polymers to close the sieve pores. An additional PBD component is the β-1,3-glucan callose produced by glucan synthase（ originally designated as glucan synthase-like, GSL）and accumulated on sieve plates. PP plugging and callose closure of sieve pores, and callose coagulation on sieve plates as well,is hypothesized to serve as a physical barrier to prevent the insects from phloem feeding. In general, plant defenses to insects are mediated by phytohormones ethylene and jasmonate, but whether both hormones have crosstalk with PBD is unclear. Therefore, the purposed study is to elucidate the regulation of PBD in wheat under attacks by aphids ,which represent a typical group of phloem-feeding insects. Up to date ,73,22 and 50 wheat genes of full length se- quences respectively coding for MYB transcription factors, GSL enzymes and lectins or their receptors have been identified up to date, but their roles in PBD are unclear. To address the quenstion, studies could first include a transcriptional screening to identify MYB, lectin （especially PP）and GSL genes involved in wheat PBD against aphids. Selected genes may be subjected to the pharmacological analysis to characterize their functions in association with ethylene or jasmonate signaling regulatory genes. Then ,the defensive functions of identified genes could be confirmed by investigating effects of gene silencing and overexpression on aphid feeding and wheat defense responses. For overexpression, MYB, PP and GSL are pertinent to be linked with genes encoding green, yellow and red fluorescence proteins （GFP, YFP and RFP）respectively, and the MYB-GFP fusion is further fused to the histidine tag （His） code. Next, fluorescent fusion proteins can be observed by laser confocal microscopy to visualize subcellular localizations supposed to be consistent with functions of the proteins in transgenic wheat. Gel mobility shift and chromatin immunoprecipitation assays could be devised to determine whether the MYB-GFP-His fusion protein,purified by His-affinitive nickel chromatography and present in the ehromatin, binds the promoter and thus activates transcription of the PP, GSL or signaling regulatory gene. Overall, these studies can elucidate signaling and transcriptional regulation of wheat PBD against aphid attacks.