Defense Transcriptome Research Articles

Expression profiling and mutant analysis reveals complex regulatory networks involved in Arabidopsis response to Botrytis infection

The expression profiles of Botrytis-inoculated Arabidopsis plants were studied to determine the nature of the defense transcriptome and to identify genes involved in host responses to the pathogen. Normally resistant Arabidopsis wild-type plants were compared with coi1, ein2, and nahG plants that are defective in various defense responses and/or show increased susceptibility to Botrytis. In wild-type plants, the expression of 621 genes representing approximately 0.48% of the Arabidopsis transcriptome was induced greater than or equal to twofold after infection. Of these 621 Botrytis-induced genes (BIGs), 462 were induced at or before 36 h post-inoculation, and may be involved in resistance to the pathogen. The expression of 181 BIGs was dependent on a functional COI1 gene required for jasmonate signaling, whereas the expression of 63 and 80 BIGs were dependent on ethylene (ET) signaling or salicylic acid accumulation, respectively, based on results from ein2 and nahG plants. BIGs encode diverse regulatory and structural proteins implicated in pathogen defense and abiotic and oxidative-stress responses. Thirty BIGs encode putative DNA-binding proteins that belong to ET response, zinc-finger, MYB, WRKY, and HD-ZIP family transcription-factor proteins. Fourteen BIGs were studied in detail to determine their role in resistance to Botrytis. T-DNA insertion alleles of ZFAR1 (At2G40140), the gene encoding a putative zinc-finger protein with ankyrin-repeat domains, showed increased local susceptibility to Botrytis and sensitivity to germination in the presence of abscisic acid (ABA), supporting the role of ABA in mediating responses to Botrytis infection. In addition, two independent T-DNA insertion alleles in the WRKY70 gene showed increased susceptibility to Botrytis. The transcriptional activation of genes involved in plant hormone signaling and synthesis, removal of reactive oxygen species, and defense and abiotic-stress responses, coupled with the susceptibility of the wrky70 and zfar1 mutants, highlights the complex genetic network underlying defense responses to Botrytis in Arabidopsis.

EST and microarray analyses of pathogen-responsive genes in hot pepper (Capsicum annuum L.) non-host resistance against soybean pustule pathogen (Xanthomonas axonopodis pv. glycines)

Large-scale single-pass sequencing of cDNA libraries and microarray analysis have proven to be useful tools for discovering new genes and studying gene expression. As a first step in elucidating the defense mechanisms in hot pepper plants, a total of 8,525 expressed sequence tags (ESTs) were generated and analyzed in silico. The cDNA microarray analysis identified 613 hot pepper genes that were transcriptionally responsive to the non-host soybean pustule pathogen Xanthomonas axonopodis pv. glycines ( Xag). Several functional types of genes, including those involved in cell wall modification/biosynthesis, transport, signaling pathways and divergent defense reactions, were induced at the early stage of Xag infiltration. In contrast, genes encoding proteins that are involved in photosynthesis, carbohydrate metabolism and the synthesis of chloroplast biogenetic proteins were down-regulated at the late stage of Xag infiltration. These expression profiles share common features with the expression profiles elicited by other stresses, such as fungal challenge, wounding, cold, drought and high salinity. However, we also identified several novel transcription factors that may be specifically involved in the defense reaction of the hot pepper. We also found that the defense reaction of the hot pepper may involve the deactivation of gibberellin. Furthermore, many genes encoding proteins with unknown function were identified. Functional analysis of these genes may broaden our understanding of non-host resistance. This study is the first report of large-scale sequencing and non-host defense transcriptome analysis of the hot pepper plant species. (The sequence data in this paper have been submitted to the dbEST and GenBank database under the codes 10227604-10236595 and BM059564-BM068555, respectively. Additional information is available at http://plant.pdrc.re.kr/ks200201/pepper.html).