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 studied intensively, 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 have negative impacts on the yields of crop plants, particularly grain legumes. 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 restructuring remain poorly characterized. Cysteine proteases are intrinsic to the genetic programmes that underpin plant development and senescence, but their functions in stress-induced senescence are not well defined. Transgenic plants including soybean that have been engineered to constitutively express phytocystatins show enhanced tolerance to a range of different abiotic stresses including drought, suggesting that manipulation of cysteine protease activities by altered phytocystatin expression in crop plants might be used to improve resilience and quality in the face of climate change.

Phytocystatins: Defense Proteins against Phytophagous Insects and Acari

“…CysProt are key enzymes in many physiological processes in plants that have to be tightly controlled. Cystatins have been related to the control of various developmental processes involving CysProt, such as the regulation of protein turnover in storage organs [14,15,16] or the senescence process mediated by abiotic stresses [17,18]. Furthermore, a defence role against pathogens and pests has been inferred to PhyCys from their up-regulation in response to biotic stress-related signals [4].…”

Rice bifunctional phytocystatin is a dual modulator of legumain and papain-like proteases

“…Current knowledge suggests that phytocystatins are the principal inhibitors of papain-like proteases (H wang et al 2009;Benchabane et al 2010;Diaz-Mendoza et al 2014;Kunert et al 2015). H owever, some larger phytocystatins possess an extra cystatin-like domain at their C-terminal, which, in barley phytocystatin, confers an in vitro ability to inhibit legumains, a different family of proteases (Martinez et al 2007).…”

“…Until recently, the majority of studies only considered the roles of group I phytocystatins in relation to papain-like proteinases (C1A) (Abe et al 1988;Belenghi et al 2003;Ohtsubo et al 2005;Martinez et al 2005Martinez et al , 2009Hong et al 2007;Hwang et al 2009), leaving a knowledge gap regarding group II phytocystatins and their possible target proteases. Despite the extensive understanding of phytocystatin involvement in developmental and stress conditions, little is known with regard to the different phytocystatins and their interactions with specific proteases in vivo (Kunert et al 2015). Thus, understanding the interactions between the inhibitors and their target proteases in the whole plant context will facilitate several applications concerning the regulation of plant proteolytic processes.…”

Review: The future of cystatin engineering

“…Cystatins are further involved in the regulation of plant developmental processes ranging from seed germination [8] to natural and abiotic stress-induced senescence (for an overview see [9]). Expression of an exogenous cystatin in a genetically modified transgenic tobacco plant limits chilling and drought sensitivity [10] and in soybean, controls shoot branching and plant growth [11].…”