Genes involved in leaf senescence and regulation of their expression

We have isolated more than a dozen cDNA clones corresponding to genes that were expressed in Arabidopsis leaves when they were kept in the dark. The nucleotide sequence analysis showed that some of the clones encoded proteins with significant homology to $\beta$-glucosidase (din2), branched-chain $\alpha$-keto acid dehydrogenase subunit E1$\beta$(din3), and another subunit E2 (din4), yeast RAD23 (din5), asparagine synthetase (din6), pre-mRNA splicing factor SRp35 (din7), phosphomannose isomerase (din9), seed imbibition protein (din10), and 2-oxoacid-dependent oxidase (din11). Accumulation of transcripts from din3,4,6 and 10 occurred rapidly after the plants were transferred to darkness. Transcripts from din2,9, and 11 could be detected only after 24 h of dark treatment. Inhibition of photo-synthesis by DCMU strongly induced the accumulation of transcripts from those genes, and application of sucrose to detached leaves suppressed the accumulation both in the dark and by DCMU. These observations indicate that expression of the genes is caused by sugar starvation resulted from the cessation of photosynthesis. We further showed that din2-encoded protein also accumulated in senescing leaves. Given these results, possible roles of din genes in leaves in the dark and senescing leaves are discussed.