Repression of six 14-3-3 protein isoforms resulting in the activation of nitrate and carbon fixation key enzymes from transgenic potato plants

Abstract

Six 14-3-3 full-size cDNAs from a potato plant were cloned and sequenced, and their high-sequence homology was established. The expression profile revealed developmental regulation and lack of organ specificity of 14-3-3 isoform synthesis in potato leaves. In order to analyse their function, transgenic plants with repression of all found isoforms were created. Since, 14-3-3 regulates in vitro assay sucrose phosphate synthase (SPS) and nitrate reductase (NR) activities, both enzyme activities and products of the interacting enzyme were analysed for transgenic plants. It was found that all transgenic lines showed significant increase in SPS and NR activities. The increase in enzyme activities was complemented by the addition of recombinant 14-3-3 protein either from potato or C. pepo. Thus, it is suggested that 14-3-3 is the main regulator of NR and SPS activities in in vivo trials and the regulatory function is isoform-independent. Sucrose and glutamate contents corresponded with the enzyme activity increase especially in case of two transgenic lines, G3.40 and G3.49, respectively. Four out of five analysed transgenic lines showed significant increase in tuber starch accumulation.