Archivio Journal of Plant Pathology

Abstract:

The development of crop varieties resistant to different pathogens is one of the most attracting perspective in breeding projects aimed at increasing host plant resistance. Since most microbial pathogens need to surmount the plant cell wall to penetrate the host tissue, the reinforcement of this compartment should increase the capacity of the host to resist pathogen attacks. One way to pursue this strategy is the enhancement of the host plant ability to inhibit or reduce the activity of cell wall degrading enzymes (CWDEs) secreted by the pathogens during the penetration and colonization of the host tissue. Polygalacturonases (PGs) are among the first CWDEs secreted by fungal pathogens during infection and in some pathosystems they are virulence factors. PGs are inhibited by the host inhibitors polygalacturonase inhibiting protein (PGIP). Moreover, PGs exhibit a reduced activity towards methylated pectin. Pectin is secreted into the cell wall in a highly methyl-esterified form and subsequently de-esterified in muro by pectin methylesterases (PMEs). Since PME activity is controlled by the pectin methylesterase inhibitor (PMEI), this inhibitor might indirectly play a role in plant defence by limiting the action of PGs secreted by microbial pathogens. By using a transgenic approach we have shown that PGIP or PMEI can endows wheat with new capacities to control the activity of fungal PGs, possibly through a direct interaction or indirectly by modifying the level and pattern of methyl esterification of cell wall pectin. Both modifications have been proven to be effective in limiting fungal disease symptom development.