Cloning, expression, and molecular characterization of a small pea gene family regulated by low levels of ultraviolet B radiation and other stresses

A pea (Pisum sativum) DNA fragment (termed MB3) was isolated by differentia l display of cDNAs obtained from total leaf RNA of ultraviolet B (UV-B) rad iation-treated plants. Longer cDNAs were cloned by rapid amplification of c DNA ends in the 3' to 5' direction. Three different, but very similar, cDNA s were cloned, sadA, sadB, and sadC, the major difference between them bein g a 36-bp deletion in the coding region of sadB. Southern blotting confirme d the occurrence of at least three genes in the pea genome. Database compar isons of the SAD protein sequences revealed high identity (46%) and similar ity (77%) with a putative tomato (Lycopersicon esculentum) short-chain alco hol dehydrogenase. Very low levels of UV-B radiation (the biologically effe ctive radiation normalized to 300 nm = 0.08 W m(-2)) was shown to up-regula te expression, a dose considerably lower than that needed to induce express ion of the well-known UV-B defensive chalcone synthase and phenylalanine am monia lyase genes. RNase protection assay revealed that primarily sadA and sadC mRNA accumulation was enhanced by UV-B. In addition to UV-B irradiatio n, ozone fumigation, wounding, aluminum stress, and salt stress induced inc reased transcript levels of the sad genes in pea.