Dark-inducible genes from Arabidopsis thaliana are associated with leaf senescence and repressed by sugars

We have isolated 5 cDNA clones (din2, din6, din9, din10 and di,lll) corresp onding to genes, the transcripts of which accumulated in leaves of Al Arabi dopsis thaliana kept in the dark. These cDNA clones encode proteins similar to beta -glucosidase (EC 3.2.1.21, din2), asparagine synthetase (EC 6.3.5. 4, din6), phosphomannose isomerase (EC 5.3.1.8, din9), seed imbibition prot ein (din10) and 2-oxoacid-dependent dioxygenases (din11). Accumulation of t he transcripts from din6 and din10 occurred within 3 h after plants were tr ansferred to darkness. The transcripts from din2, din9 and din11 were only detected after 24 h of dark treatment. We also observed the accumulation of the dill transcripts in senescing leaves. Application of a photosynthesis inhibitor, 3-(3,4-dichlorophenyl)-1-1-dimethyl-urea, induced the expression of the dill genes under illumination. Application of sucrose to detached l eaves suppressed the accumulation of the dill transcripts in the dark. Thes e results indicate that expression of these genes partly depends on cellula r sugar level, The sugar-modulated expression of the dill genes suggests th at dark-induced expression of these genes might be related to sugar starvat ion occurring in leaf cells in the dark, when the photosynthesis is hindere d.