Abstract

Jasmonic acid (JA) and its derivatives occur naturally in Arabidopsis thaliana ( A. thaliana ), and regulate the expression of a number of genes such as the ones involved in flowering, defence response and senescence. Additionally, precursors and downstream components of the JA pathway have been shown to elicit some of the responses previously attributed to JA. Of interest to our lab was to investigate the effect of a compound downstream of JA, 12-hydroxyhjasmonate (12-OHJA), on gene expression as well as the phenotypic effect of accumulating higher internal levels of the compound. This was based on previous data showing that, while most genes are co-regulated by JA and 12-OHJA, Thi2.1 , one of the marker genes of JA induction, is not upregulated upon 12-OHJA treatment. Furthermore, exogenous application of this compound shares only some of the phenotypes of JA. In order to gain further insight into the molecular function of the two compounds, we investigated the effects of 4h treatments with each compound on gene expression using the Affymetrix® A. thaliana full genome array. The data demonstrates that there are subsets of genes that are specifically induced or repressed by each of the two compounds, pointing to the possibility of two differentially regulated pathways. 12-OHJA was recently shown to be sulfonated in vitro by one of the eighteen A. thaliana sulfotransferases, AtST2a (Gidda et al, 2003). To gain further insight of the function of AtST2a and its homologous gene AtST2b (whose substrate is yet to be identified), knockout plants in each of the genes were isolated and subjected to phenotypic analyses. The results demonstrate that the AtST2b -KO mutant flowers earlier and has more leaves than wildtype or AtST2a -KO under short days. Combined with metabolite analysis of mutants, the data suggests that another compound, maybe an isomer of 12-OHJA, is responsible for the control of flowering time in short days.