Constitutive Expression of a XEGIP in Potato Results in Phenotypic Changes Suggesting Endogenous Inhibition of Cell Wall Growth

One mechanism for plant defense is the production of proteinaceous inhibitors that block the function of pathogen-produced cell wall-modifying enzymes. The xyloglucanase-specific endoglucanase inhibitor protein (XEGIP) is proposed to exist principally to block pathogen family 12 xyloglucan-specific endoglucanases. The role of XEGIP in plant defense was tested by generating transgenic XEGIP-overexpressing potato plants. Overexpression of an endogenous XEGIP in potato resulted in major changes in plant phenotype. Short petioles, small, thick leaves, reduced root formation, and distorted tuber shape resulted from XEGIP overexpression. Susceptibility to late blight, caused by Phytophthora infestans, was not altered. For the XEGIP tested (AY321357), there are previously unreported alterations in plant development that can be attributed to constitutive expression of XEGIP. The principal role of at least this XEGIP may be regulation of plant-encoded enzymes.