Transcript level regulation of the vacuolar H+-ATPase subunit isoforms VHA-a, VHA-E and VHA-G in Arabidopsis thaliana

The presence of isogenes encoding V- ATPase subunits seems to be a characteristic for plants. Twenty- eight genes encode for the 13 different subunits in Arabidopsis thaliana, 23 genes each are known in tomato ( Solanum lycopersicum) and can be identified in rice ( Oryza sativa), respectively. In Arabidopsis the four subunits VHA- B, - E, - G and - a are encoded by three isogenes each. The transcript levels of these subunits were analysed by in silico evaluation of transcript pattern derived from the NASC- array database and exemplarily confirmed by semiquantitative RT- PCR. A tissue specifity was observed for the isoforms of VHA- E and VHA- G, whereas expression of VHA- a isoforms appeared independent of the tissue. Inflicting environmental stresses upon plants resulted in differentiated expression patterns of VHA- isoforms. Whereas salinity had minor effect on the expression of V- ATPase genes in A. thaliana, heat and drought stress led to alterations in transcript amount and preference of isoforms. Correlation analysis identified two clusters of isoforms, which were co- regulated on the transcript level.