Antisense inhibition of cytosolic NADP-dependent isocitrate dehydrogenase in transgenic potato plants

Cytosolic NADP-dependent isocitrate dehydrogenase (cyt-NADP-ICDH; EC 1.1.1.42) has been suggested to play a major role in the production of 2-oxoglutarate, an important precursor for amino acid synthesis. Using an antisense RNA approach under the control of the cauliflower mosaic virus 35S promoter, transgenic potato plants were created in which NADP-ICDH activity was reduced to 8% of the wild-type level in leaves. Residual activity was almost completely due to mitochondrial and chloroplastic NADP-ICDH isoforms. Activity staining after non-denaturing polyacrylamide gel electrophoresis revealed the complete absence of a major activity band in leaves of antisense plants. No differences in growth or development, including flower formation and tuber yield, were observed between transgenic and wild-type plants. Photosynthesis and respiration were also unchanged. Levels of amino acids were the same in wild-type and cyt-NADP-ICDH antisense plants, even when accumulation of amino acids was induced by incubation of detached leaves in tap water in the dark (`induced senescence'). Consistent with a reduction in NADP-ICDH activity, however, were slight increases in the levels of isocitrate (up to 2.5-fold) and citrate (up to 2-fold). 2-Oxoglutarate was not reduced. Our data indicate that potato plants can cope with a severe reduction in cyt-NADP-ICDH activity without major shifts in growth and metabolism.