Cloning and characterization of leaf senescence up-regulated genes in sweet potato

Genes that are expressed during leaf senescence in sweet potato (Ipomoea ba tatas, cv. Tainong 57) were identified by the isolation of cDNA fragments w ith the mRNA differential display method. Eight senescence-associated cDNA clones for mRNAs differentially expressed during leaf senescence were obtai ned and characterized. Northern blot analysis indicated that all these clon es represented genes that are up-regulated during natural leaf senescence. Among them, five cDNA clones have been obtained in full length by screening a senescing leaf cDNA library or by performing rapid amplification of cDNA ends. DNA and protein database searches revealed that clones SPA15 and SPC 9 encode proteins of unknown function. The other six clones SPG31, SPC20, S PG27, SPC25, SPC15 and SPC1 showed significant sequence homology to known g enes encoding a cysteine proteinase, isocitrate lyase, S-adenosylmethionine decarboxylase, cysteine proteinase inhibitor and metallothionein-like type I protein. The gene expression patterns represented by SPG31, SPG27 and SP A15 were found to be highly specific in senescing leaves. The corresponding transcripts for SPG31, SPG27 and SPA15 were below detectable levels in oth er organs such as flowers, stems, roots and tubers. The possible physiologi cal roles of these gene products in the leaf senescence process are discuss ed.