DOES THE TYPE III SECRETION SYSTEM OF RHIZOBIUM SPECIES NGR234 AFFECT THE DEFENCE RESPONSE IN PLANT LEAVES?

摘要

A successful interaction between rhizobial cells and their corresponding host plant results in newly formed organs hosting actively nitrogen fixing bacteria. The bacteria signal their presence via Nod factors to initiate specialized plant developmental programs. Infection threads are formed and at the same time there is activation of cell division at the site of the future nodule. The whole process is highly regulated and more is now known to understand why plants initiate root hair deformation onlyin the presence of their compatible symbiont, more puzzling are the mechanisms contributing to bacteria persistence in plant tissues. Pathogenic bacteria with a biotrophic lifestyle develop strategies to subvert obvious and well characterized plant defences, while they multiply in the host. In rhizobial symbiosis, several reports mention plant responses that are normally associated with molecular defence mechanisms (Mithofer 2002 for review). However, these showed that a plant defence response may occur in legumes undergoing rhizobial symbiosis. Whether it genuinely limits nodulation or rhizobia progression towards active nodule formation remains unknown.