Repression of some cysteine-proteases makes barley leaves more resistant to pest and pathogens

To survive under stress conditions, plants alter gene expression patterns, make structural and physiological adjustments and optimize the efficient use of resources. Among these changes, protein turn-over is required for a rapid degradation of proteins and an effective nutrient recycling. Consequently, some protease encoding genes are induced and a coordinated proteolytic process take place. In barley, four C1A cysteine proteases are up-regulated under water deficit regime in leaves, including HvPap-1 and HvPap-19 genes. Unexpected changes in leaf cuticle thickness and stomata pore area were observed in knock-down lines for these two genes. In parallel, the efficiency of the photosystem II and the amount of total proteins was almost unaltered in drought-stressed transgenic leaves while both parameters diminished in stressed WT plants. The proteolytic pattern activities in knock-down lines did not changed but the amino acid accumulation increased in response to drought stress, concomitant to a higher ABA content. JA and JA-Ile concentration was also increased in stressed leaves of WT and HvPap-1 knock-down leaves, but their levels were lower in HvPap-19 knock-down lines, demonstrating a specific hormonal crosstalk of the process. Structural and physiological changes have important effects in plant defence responses not only to drought stress but also to fungal infection by Magnaporthe oryzae and the feeding of the phytophagous spider mite Tetranychus urticae.