Differential expression of senescence-associated mRNAs during leaf senescence induced by different senescence-inducing factors in Arabidopsis.

Four cDNA clones, named pSEN2, pSEN3, pSEN4, and pSEN5, for mRNAs induced during leaf senescence in Arabidopsis thaliana were characterized. The clones were isolated from a cDNA library of detached leaves incubated in darkness for 2 days to accelerate senescence, first by differential screening and then by examining expression of the primarily screened clones during age-dependent leaf senescence. Transcript levels detected by these cDNA clones, thus, were up-regulated in an age-dependent manner and during dark-induced leaf senescence. In contrast, when leaf senescence was induced by ethylene, ABA or methyljasmonate, the transcript level detected by the clones was differentially regulated depending on the senescence-inducing hormones. The transcript level for pSEN4 increased during senescence induced by all three hormones, while the transcript detected by the pSEN2 clone did not increase during senescence induced by ethylene. The transcript level for pSEN5 was increased upon ABA-induced senescence but decreased during ethylene-induced senescence. The pSEN3 clone detected multiple transcripts that are differentially regulated by these factors. The results show that, although 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 transferase. This result is consistent with the expected roles of senescence-induced genes during leaf senescence.