Emerging Roles of beta-Glucanases in Plant Development and Adaptative Responses

Plant beta-glucanases are enzymes involved in the synthesis, remodelling and turnover of cell wall components during multiple physiological processes. Based on the type of the glycoside bond they cleave, plant beta-glucanases have been grouped into three categories: (i) beta-1,4-glucanases degrade cellulose and other polysaccharides containing 1,4-glycosidic bonds to remodel and disassemble the wall during cell growth. (ii) beta-1,3-glucanases are responsible for the mobilization of callose, governing the symplastic trafficking through plasmodesmata. (iii) beta-1,3-1,4-glucanases degrade mixed linkage glucan, a transient wall polysaccharide found in cereals, which is broken down to obtain energy during rapid seedling growth. In addition to their roles in the turnover of self-glucan structures, plant beta-glucanases are crucial in regulating the outcome in symbiotic and hostile plant-microbe interactions by degrading non-self glucan structures. Plants use these enzymes to hydrolyse beta-glucans found in the walls of microbes, not only by contributing to a local antimicrobial defence barrier, but also by generating signalling glucans triggering the activation of global responses. As a counterpart, microbes developed strategies to hijack plant beta-glucanases to their advantage to successfully colonize plant tissues. This review outlines our current understanding on plant beta-glucanases, with a particular focus on the latest advances on their roles in adaptative responses.