Abstract

A main interest of our laboratory is to characterize the function of the 17 sulfotransferase-coding genes of Arabidopsis thaliana. The purpose of my project is to elucidate the biochemical and biological functions of AtST4c, a member of the AtST4 subfamily (AtST4a, b and c). AtST4c knockout plants were found to exhibit a photoperiod-independent early flowering phenotype suggesting that AtST4c plays a negative role in flowering induction. In addition, AtST4c knockout plants produced shorter primary roots, a reduced number of lateral roots, slightly smaller rosettes, fewer seeds per silique and finally smaller seeds, suggesting that AtST4c plays a positive role in Arabidopsis growth. Transcript expression studies showed that AtST4c is mainly expressed in roots and is repressed by the cytokinin trans-zeatin suggesting that the positive effect of AtST4c on plant growth is repressed by the cytokinin signaling pathway in Arabidopsis.
In order to further characterize the role of AtST4c in the control of flowering time, the expression of floral integrator genes such as LEAFY, SUPPRESSOR OF OVEREXPRESSION OF CO 1(SOC1) and APETALA 1 was studied in AtST4c mutant plants. Our results show up-regulation of LEAFY and APETALA 1 in the mutant plants suggesting that AtST4c acts upstream of these two important meristem identity genes. However, no changes in SUPPRESSOR OF OVEREXPRESSION OF CO 1(SOC1) expression were observed suggesting that the early flowering phenotype is independent of four of the five pathways that promote flowering in Arabidopsis. Taken together our results suggest that AtST4c participates in the control of flowering time via the aging pathway or by interfering with the repression mediated by the gene TERMINAL FLOWER 1.
To characterize the biochemical function of AtST4c, we compared the sulfated meatbolome of AtST4c knockout mutant plants and wild-type plants using liquid chromatography-mass spectrometry. Using this approach we were able to propose a structure for the substrate of AtST4c.