The protein phosphatase 2A catalytic subunit StPP2Ac2b acts as a positive regulator of tuberization induction in Solanum tuberosum L.
This study provides the first genetic evidence for the role of PP2A in tuberization, demonstrating that the catalytic subunit StPP2Ac2b positively modulates tuber induction, and that its function is related to the regulation of gibberellic acid metabolism.  The results contribute to a better understanding of the molecular mechanism controlling tuberization induction, which remains largely unknown.  The serine/threonine protein phosphatases type 2A (PP2A) are implicated in several physiological processes in plants, playing important roles in hormone responses.  In cultivated potato (Solanum tuberosum), six PP2A catalytic subunits (StPP2Ac) were identified.  The PP2Ac of the subfamily I (StPP2Ac1, 2a and 2b) were suggested to be involved in the tuberization signaling in leaves, where the environmental and hormonal signals are perceived and integrated.  The aim of this study was to investigate the role of PP2A in the tuberization induction in stolons.  We selected one of the catalytic subunits of the subfamily I, StPP2Ac2b, to develop transgenic plants overexpressing this gene (StPP2Ac2b-OE).  Stolons from StPP2Ac2b-OE plants show higher tuber induction rates in vitro, as compared to wild type stolons, with no differences in the number of tubers obtained at the end of the process.  This effect is accompanied by higher expression levels of the gibberellic acid (GA) catabolic enzyme StGA2ox1.  GA up-regulates StPP2Ac2b expression in stolons, possibly as part of the feedback system by which the hormone regulates its own level.  Sucrose, a tuber-promoting factor in vitro, increases StPP2Ac2b expression.  We conclude that StPP2Ac2b acts in stolons as a positive regulator tuber induction, integrating different tuberization-related signals mainly though the modulation of GA metabolism.