DEVELOPMENTAL AND ENVIRONMENTAL-REGULATION OF 2 RIBOSOMAL-PROTEIN GENES IN TOBACCO

Two cDNA clones, TSC29 and TSC40, were isolated from a cDNA library pr epared from three-day-old tobacco cell suspension grown to early expon ential stage. DNA sequence analyses and database searches revealed tha t the TSC29 transcript encodes a protein which is highly homologous to eukaryotic 60S ribosomal (r)-protein L25 and that the TSC40 product i s homologous to rat 60S r-protein L34. Southern blot analysis showed t hat the putative r-protein genes are members of multigene families. Tr anscript levels of both genes were most abundant in three-day-old cell suspension and declined in older cultures. Transcripts were also pres ent in plant vegetative and reproductive organs. However, for TSC40 in particular, the mRNA levels were lower in plant organs than in three- day-old cell suspension. Stems and roots exhibited higher expression t han leaves and flowers, indicating that these clones are differentiall y regulated in various cell types. Both genes were expressed at low le vels in mature seeds but transcript levels significantly increased aft er one day of germination, remained at a high level until day 4, and d eclined after day 5. In situ localization experiments with germinating seedlings revealed that the TSC29 transcript was preferentially local ized in root tips, epidermis, and endosperm. Wounding increased the st eady-state mRNA amounts of these r-protein genes, and 2,4-dichlorophen oxyacetic acid and benzyladenine further increased the transcript leve l.