Salicylic Acid and a Chitin Elicitor Both Control Expression of the CAD1 Gene Involved in the Plant Immunity of Arabidopsis

The Arabidopsis mutant cad1 (constitutively activated cell death 1) shows a phenotype that mimics hypersensitive response (HR)-like cell death. The CAD1 gene, which encodes a protein containing a domain with significant homology to the MACPF (membrane attach complex and perforin) domain of complement components and perforin, is likely to control plant immunity negatively and has a W-box cis-element in its promoter region. We found that expression of the CAD1 gene and other W-box containing genes, such as NPR1 and PR2, was promoted by salicylic acid (SA) and benzothiadiazole (BTH) as a SA agonist. The CAD1 gene was also stimulated by a purified chitin oligosaccharide elicitor (degree of polymerization = 8). This latter control was not under SA, because CAD1 expression was not suppressed in 35SnahG transgenic plants, which are unable to accumulate SA. These expression profiles were confirmed by promoter analysis using pCAD1::GUS transgenic plants. The CAD1 expression promoted by BTH and the chitin elicitor was not suppressed in the npr1 mutant, which is insensitive to SA signaling. These results indicate that the CAD1 gene is regulated by two distinct pathways involving SA and a chitin elicitor: viz., SA signaling mediated through an NPR1-independent pathway, and chitin elicitor signaling, through an SA-independent pathway. Three CAD1 homologs that have multiple W-box elements in their promoters were also found to be under the control of SA.     

WRKY转录因子与植物逆境响应

WRKY转录因子是高等植物特有的一类转录调控因子,也是植物生命活动中不可或缺的调控枢纽。研究发现,WRKY转录因子参与植物生长发育过程及多种生物与非生物逆境响应。本文分析了WRKY转录因子的分类及结构,对其多种作用机制包括上游调控、下游调控、蛋白质相互作用等进行了归类,总结了近年来在各类植物上发现的WRKY转录因子调控植物生长发育和参与植物响应生物及非生物逆境的多重功能。并针对目前WRKY转录因子的研究所存在的问题,提出部分意见,为进一步挖掘WRKY家族的功能机制奠定了基础。     

真核藻类WRKY基因家族的鉴定及表达分析北大核心CSCD

WRKY是植物特有的一个转录因子超家族,参与植物生长发育、物质代谢以及生物和非生物胁迫响应等多种生物学过程的调控。尽管WRKY转录因子基因已在高等植物广泛表征,然而有关真核藻类WRKY却知之甚少。采用多序列比对、系统进化和保守域分析等技术对30种真核藻类WRKY进行全基因组鉴定,共获得24个WRKY成员,均来自绿藻门(Chlorophyta)藻类。红藻门(Rhodophyta)、灰藻门(Glaucophyta)和硅藻门(Bacillariophyta)等藻类未检测到WRKY。24个WRKY成员均具有保守结构域七肽序列WRKYGQ(E/A/H/N)K和锌指基序C-X4-5-C-X22-23-H-X-H,分别归类于Ⅰ、Ⅱa、Ⅱb和R组。高含虾青素的雨生红球藻(Haematococcus pluvialis)含有2个Ⅰ类WRKY成员(HaeWRKY-1和HaeWRKY-2)。进一步克隆HaeWRKY-1和HaeWRKY-2基因编码序列,构建原核表达载体在大肠杆菌BL21(DE3)中诱导表达,并通过Ni-NTA亲和层析获得纯化的HaeWRKY融合蛋白。雨生红球藻在正常培养条件下,HaeWRKY-1表达量显著高于HaeWRKY-2。高光逆境胁迫显著上调HaeWRKY-1表达和下调HaeWRKY-2表达。HaeWRKY基因启动子含有多个光、乙烯、脱落酸(abscisic acid, ABA)以及逆境响应顺式元件。特别在HaeWRKY-2启动子区未检测到W-box顺式元件,但HaeWRKY-1和控制虾青素生物合成关键酶基因HaeBKT、HaePSY基因启动子含有W-box元件。基于本研究及前人的发现,我们推测高光胁迫下HaeWRKY-2低表达可能导致HaeWRKY-1的上调表达,HaeWRKY-1进而上调虾青素合成关键基因(HaeBKT、HaePSY等)表达,促进虾青素合成积累。这为深入解析雨生红球藻高光胁迫响应及虾青素合成的调控机制提供了新思路。