Expression analysis of Arabidopsis thaliana NAD-dependent isocitrate dehydrogenase genes shows the presence of a functional subunit that is mainly expressed in the pollen and absent from vegetative organs

NAD-dependent isocitrate dehydrogenase (IDH) is a Krebs cycle enzyme situated in mitochondria. In Arabidopsis thaliana, five genes encode functional IDH sub-units that can be classed into two groups based on gene structure and subunit amino acid sequence. Arabidopsis contains two 'catalytic' and three 'regulatory' subunits according to their homology with yeast IDH. To date, an active IDH is believed to be heteromeric, containing at least one of each subunit type. This was verified in Arabidopsis by the complementation of yeast IDH mutants with the different Arabidopsis IDH-encoding cDNAs. Indeed, a single 'catalytic' and 'regulatory' subunit was sufficient to restore acetate growth of the yeast IDH double mutant. To gain information on possible IDH subunit interactions in planta, Arabidopsis IDH gene expression was analysed by Northern blot, PCR on cDNA libraries, in silico and in 'promoter'-reporter gene transgenic plants. Four of the IDH genes were expressed in all plant organs tested, while one gene (At4g35650) was not expressed in vegetative organs but was mainly expressed in the pollen. In leaves, the IDH genes were highly expressed in the veins, and to a lesser extent in mesophyll cells. The data are discussed with respect to IDH in other plant species.