Up-regulation of a stress-responsive endochitinase VvChit-IV in grapevine cell cultures improves in vitro stress tolerance.

Chitinases are pathogenesis-related proteins, which play an important role in plant growth regulation, defense mechanism, and stress tolerance. Embryogenic cultures from Vitis vinifera cv. Tempranillo exposed to in vitro stress exhibited the expression of an extracellular class IV endochitinase VvChit-IV. Phylogenetic and conserved motif analyses provided insights into the evolutionary relationships of chitinases. A computation-based investigation showed conserved domains and illustrated a chitin-binding site for chitin cleavage with a catalytic domain of glycoside hydrolase. Interestingly, gene expression pattern showed a differential expression of VvChit-IV associated with embryonic stress response to in vitro conditions. In response to in vitro stress, transcript level of VvChit-IV increased in embryogenic calli and cell suspensions and peaked at 1.5 and 3 folds, respectively, when compared to an internal reference gene. Evidence of tissue culture stress-induced endochitinase was reported here for the first time indicating that in vitro stress could mitigate elicitor application to induce chitinase expression and can stimulate an immune response against abiotic constraints. Data showed that up-regulation of VvChit-IV was associated with a substantial increase of H2O2 and proline without significant change in malondialdehyde content suggesting that the H2O2 signaling network might trigger a priming effect to boost the defense response against environmental stress. Endochitinase activation in plant stress mitigation was thus highlighted to improve tolerance through attenuation of oxidative stress. This study revealed that the grapevine endochitinase is promising for enhancing coping-oriented adaptation and abiotic stress tolerance, which gives new insights into its feasibility for use in cross-tolerance and crop improvement.