MPMI Proposal Institute of Plant Biology , Master student, R98B42021 Topic T o define the mechanism s of stress i mprint in plants Background and rationale A history of exposure to a range of different types of stress alters subsequent plant responses. The process of priming or hardening involv es prior exposure to a biotic or a n abiotic stress factor making a plant more resistant to future exposure. This feature, in higher plants, indicates some capacity for memory. Sustained alterations in levels ofkey signalling metabolites or transcription factors could provide an expl anation for how plant metabolism is altered by exposure to various stresses. Alternatively epigen etic changes could play a role by enabling long-term changes in gene expression. Exposure to a priming agent could activate a gene or set of genes but instead of reverting to the transcriptionally silent state once the stimulus is removed, an epigenetic mark could perhaps be left, keeping the region in a permissive state, facilita ting quicker and more potent responses to subsequent attacks. In the stress responses, defence genes show the primingphenomenon; they are able to respond f aster and to a greater extent to subsequent challenge. The promoter s of many of these defence genes contain at least one W-boxthat provides binding sites for WRKY transcription factors . Genes encoding WRKY factors are themselves transcriptionally induced by either pathogen inf ection or treatme nt with microbe-associated molecul ar patterns, such as flagellin. Chromatin structure is important for the regulation of gene expression. Acetylation of lysines in the amino-terminal tails of histones H3 and H4 has been associated with active genes. This modification reduces the ionic interaction between positively charged lysine side chains and the negativ ely charged D NA backbone. Moreover , lysine acet ylation provides docking sites for transcriptional coactivator proteins. The strongest correlation between histone methylation and gene act ivity is found for trimethylation of Lys 4 on histone H3 (H3K4me3) on promoters and coding sequences of active genes. Although gene priming is a widespr ead phenomenon and h as also been described for the defence response in animals, little i s known
