Potential use of phytocystatins in crop improvement, with a particular focus on legumes

Abstract

Phytocystatins are a well-characterized class of naturally-occurring protease inhibitors that function by preventing the catalysis of papain-like cysteine proteases. The action of cystatins in biotic stress resistance has been intensively studied but relatively little is known about their functions in plant growth and defence responses to abiotic stresses, such as drought. Extreme weather events such as drought and flooding will become more frequent as a result of climate change. The concepts that changes in cellular protein content and composition are required for acclimation to different abiotic stresses and that these adjustments are achieved through regulation of proteolysis are widely accepted. However, the nature and regulation of the protein turnover machinery that underpins essential stress-induced cellular re-structuring remains poorly characterised. Cysteine proteases are intrinsic to the genetic programs that underpin developmental senescence, but their functions in stress-induced senescence are poorly defined. While much remains uncertain regarding the individual cysteine protease targets of endogenous cystatins and their precise functions in the regulation of physiological processes are largely unknown, current evidence suggests that manipulation of cysteine protease activities by engineered cystatin expression might be used for to improve the resilience and quality of crop plants in the face of climate change.