DIFFERENTIAL EXPRESSION OF SENESCENCE-ASSOCIATED MESSENGER-RNAS DURING LEAF SENESCENCE INDUCED BY DIFFERENT SENESCENCE-INDUCING FACTORS IN ARABIDOPSIS

Four cDNA clones, named pSEN2, pSEN3, pSEN4, and pSEN5, for mRNAs indu ced during leaf senescence in Arabidopsis thaliana were characterized. The clones were isolated from a cDNA library of detached leaves incub ated in darkness for 2 days to accelerate senescence, first by differe ntial screening and then by examining expression of the primarily scre ened clones during age-dependent leaf senescence. Transcript levels de tected by these cDNA clones, thus, were up-regulated in an age-depende nt manner and during dark-induced leaf senescence. In contrast, when l eaf senescence was induced by ethylene, ABA or methyljasmonate, the tr anscript level detected by the clones was differentially regulated dep ending on the senescence-inducing hormones. The transcript level for p SEN4 increased during senescence induced by all three hormones, while the transcript detected by the pSEN2 clone did not increase during sen escence induced by ethylene. The transcript level for pSEN5 was increa sed upon ABA-induced senescence but decreased during ethylene-induced senescence. The pSEN3 clone detected multiple transcripts that are dif ferentially regulated by these factors. The results show that, althoug h the apparent senescence symptoms of Arabidopsis leaf appear similar regardless of the senescence-inducing factors, the detailed molecular state of leaf cells during senescence induced by different senescence- inducing factors is different. The pSEN3 clone encodes a polyubiquitin and the pSEN4 clone encodes a peptide related to endoxyloglucan trans ferase. This result is consistent with the expected roles of senescenc e-induced genes during leaf senescence.