RESUMEN
Protein breakdown and mobilization are some of the major metabolic features associated with abiotic stresses, essential for nutrient recycling and plant survival. Genetic manipulation of protease and/or protease inhibitors may contribute to modulate proteolytic processes and plant responses. The expression analysis of the whole cystatin family, inhibitors of C1A cysteine proteases, after water deprivation in barley leaves highlighted the involvement of Icy-2 and Icy-4 cystatin genes. Artificial microRNA lines independently silencing the two drought-induced cystatins were generated to assess their function in planta. Phenotype alterations at the final stages of the plant life cycle are represented by the stay-green phenotype of silenced cystatin 2 lines. Besides, the enhanced tolerance to drought and differential responses to water deprivation at the initial growing stages are observed. The mutual compensating expression of Icy-2 and Icy-4 genes in the silencing lines pointed to their cooperative role. Proteolytic patterns by silencing these cystatins were concomitant with modifications in the expression of potential target proteases, in particular, HvPap-1, HvPap-12, and HvPap-16 C1A proteases. Metabolomics analysis lines also revealed specific modifications in the accumulation of several metabolites. These findings support the use of plants with altered proteolytic regulation in crop improvement in the face of climate change.