ANTISENSE EXPRESSION OF A SUCROSE NON-FERMENTING-1-RELATED PROTEIN-KINASE SEQUENCE IN POTATO RESULTS IN DECREASED EXPRESSION OF SUCROSE SYNTHASE IN TUBERS AND LOSS OF SUCROSE-INDUCIBILITY OF SUCROSE SYNTHASE TRANSCRIPTS IN LEAVES

This report describes the analysis of transgenic potato plants stably transformed with chimeric genes comprising either a patatin (tuber-spe cific) or a ST-LS1 (leaf- and stem-specific) gene promoter and a potat o sucrose non-fermenting-1 (SNF1)-related protein kinase gene (PKIN1) sequence in the antisense orientation. Presence of the transgene was c onfirmed by Southern analysis. The transformants were screened using a peptide kinase activity assay for SNF1 related activity and/or Northe rn blot analysis, and two independent transgenic lines from each trans formation, PAT 1.3, PAT 1.10, LS 1.4 and LS 1.11, were selected. Antis ense PKIN1 transcripts were detectable in all four of the selected lin es, and measurements made using the specific peptide phosphorylation a ssay showed that SNF1 related protein kinase activity had decreased in both PAT 1.3 and PAT 1.10 compared with controls. SNF1 regulates the expression of many genes encoding enzymes of carbohydrate metabolism i n yeast. In order to investigate an analogous role for PKIN1, the acti vities of fructokinase, glucokinase, neutral and acid invertase and su crose synthase in the tubers of PAT 1.3 and PAT 1.10 were compared wit h those in wild-type controls. Sucrose synthase activity was decreased to 36% of wild-type activity in tubers of PAT 1.10, and sucrose synth ase transcript levels were decreased in tubers of both PAT 1.3 and PAT 1.10. Activities of the other enzymes were unaffected. Leaves of line s LS 1.4, LS 1.11 and controls were then excised and cultured on a med ium containing 250 mM sucrose. This treatment induced sucrose synthase gene expression in the control leaves but not those of the transgenic lines. This finding is the first demonstration of a role for SNF1-rel ated protein kinases in the regulation of carbohydrate metabolism of h igher plants.