Towards a function for an Arabidopsis protein involved in sucrose dynamics

Sammanfattning: System based models of plants rely on descriptions and assigned functions of genes, and currently 50% of the genes in Arabidopsis thaliana has either no assigned function or a function based on homology only. Mitogen activated protein kinases (MAPK's) are key players in cell signalling and are conserved among eukaryotes, though their targets are highly diverse. A recent study has described a small Arabidopsis protein (80), without homology to any described protein, as a phosphorylation target of the MAPK's MPK3/6. Further work established α-glucan phosphorylase (PHS) as interacting with 80 and described a delayed senescence phenotype for 80 knock-out plants. This work has examined the effect of flagellin and sucrose on the stability of the 80 protein in seedling culture. In whole plants the effect of 80 on glucose, sucrose and the glucose residue content of the soluble heteroglycan (SHG) pool, as well as 80's stability during senescence has been investigated. 80 was found to be degraded under induced leaf senescence, in a way similar to that of induced darkness in whole plant systems. At day-time leaves from 80knock-out plants exhibited an increase in sucrose and no changes in glucose content. At night-time 80knock-out plants exhibited an increased sucrose:glucose ratio. 80knock-out leaves did not exhibit significant changes in sucrose and glucose content during senescence. In seedlings, 80 was found to be stabilised by sucrose and flagellin, though the sucrose dependent stabilisation was partly inhibited by flagellin.