A triticale water-deficit-inducible phytocystatin inhibits endogenous cysteine proteinases in vitro

The roles of plant proteases and protease inhibitors in drought response: a review

Upon exposure to drought, plants undergo complex signal transduction events with concomitant changes in the expression of genes, proteins and metabolites. For example, proteomics studies continue to identify multitudes of drought-responsive proteins with diverse roles in drought adaptation. Among these are protein degradation processes that activate enzymes and signalling peptides, recycle nitrogen sources, and maintain protein turnover and homeostasis under stressful environments. Here, we review the differential expression and functional activities of plant protease and protease inhibitor proteins under drought stress, mainly focusing on comparative studies involving genotypes of contrasting drought phenotypes. We further explore studies of transgenic plants either overexpressing or repressing proteases or their inhibitors under drought conditions and discuss the potential roles of these transgenes in drought response. Overall, the review highlights the integral role of protein degradation during plant survival under water deficits, irrespective of the genotypes' level of drought resilience. However, drought-sensitive genotypes exhibit higher proteolytic activities, while drought-tolerant genotypes tend to protect proteins from degradation by expressing more protease inhibitors. In addition, transgenic plant biology studies implicate proteases and protease inhibitors in various other physiological functions under drought stress. These include the regulation of stomatal closure, maintenance of relative water content, phytohormonal signalling systems including abscisic acid (ABA) signalling, and the induction of ABA-related stress genes, all of which are essential for maintaining cellular homeostasis under water deficits. Therefore, more validation studies are required to explore the various functions of proteases and their inhibitors under water limitation and their contributions towards drought adaptation.

Proteolytic and Structural Changes in Rye and Triticale Roots under Aluminum Stress

Proteolysis and structural adjustments are significant for defense against heavy metals. The purpose of this study was to evaluate whether the Al³⁺ stress alters protease activity and the anatomy of cereale roots. Azocaseinolytic and gelatinolytic measurements, transcript-level analysis of phytocystatins, and observations under microscopes were performed on the roots of Al³⁺-tolerant rye and tolerant and sensitive triticales exposed to Al³⁺. In rye and triticales, the azocaseinolytic activity was higher in treated roots. The gelatinolytic activity in the roots of rye was enhanced between 12 and 24 h in treated roots, and decreased at 48 h. The gelatinolytic activity in treated roots of tolerant triticale was the highest at 24 h and the lowest at 12 h, whereas in treated roots of sensitive triticale it was lowest at 12 h but was enhanced at 24 and 48 h. These changes were accompanied by increased transcript levels of phytocystatins in rye and triticale-treated roots. Light microscope analysis of rye roots revealed disintegration of rhizodermis in treated roots at 48 h and indicated the involvement of root border cells in rye defense against Al³⁺. The ultrastructural analysis showed vacuoles containing electron-dense precipitates. We postulate that proteolytic-antiproteolytic balance and structural acclimation reinforce the fine-tuning to Al³⁺.

Sugarcane cystatins: From discovery to biotechnological applications

Phytocystatins are tight-binding cysteine protease inhibitors produced by plants. The first phytocystatin described was isolated from Oryza sativa and, since then, cystatins from several plant species were reported, including from sugarcane. Sugarcane cystatins were unraveled in Sugarcane EST project database, after sequencing of cDNA libraries from various sugarcane tissues at different developmental stages and six sugarcane cystatins were cloned, expressed and characterized (CaneCPI-1 to CaneCPI-6). These recombinant proteins were produced in different expression systems and inhibited several cysteine proteases, including human cathepsins B and L, which can be involved in pathologies, such as cancer. In this review, we summarize a comprehensive history of all sugarcane cystatins, presenting an updated phylogenetic analysis; chromosomal localization, and genomic organization. We also present protein docking of CaneCPI-5 in the active site of human cathepsin B, insights about canecystatins structures; recombinant expression in different systems, comparison of their inhibitory activities against human cysteine cathepsins B, K, L, S, V, falcipains from Plasmodium falciparum and a cathepsin L-like from the sugarcane weevil Sphenophorus levis; and enlighten their potential and current applications in agriculture and health.

Recombinant cystatins in plants

Dozens of studies have assessed the practical value of plant cystatins as ectopic inhibitors of Cys proteases in biological systems. The potential of these proteins in crop protection to control herbivorous pests and pathogens has been documented extensively over the past 25 years. Their usefulness to regulate endogenous Cys proteases in planta has also been considered recently, notably to implement novel traits of agronomic relevance in crops or to generate protease activity-depleted environments in plants or plant cells used as bioreactors for recombinant proteins. After a brief update on the basic structural characteristics of plant cystatins, we summarize recent advances on the use of these proteins in plant biotechnology. Attention is also paid to the molecular improvement of their structural properties for the improvement of their protease inhibitory effects or the fine-tuning of their biological target range.

Physiological and proteomic analysis of maize seedling response to water deficiency stress

Low water availability is a major abiotic factor limiting photosynthesis and the growth and yield of crops. Maize (Zea mays) is among the most drought-sensitive cereal crops. Herein, the physiological and proteomic changes of maize seedlings caused by polyethylene-glycol-induced water deficit were analyzed. The results showed that malondialdehyde and proline contents increased continuously in the treated seedlings. Soluble sugar content and superoxide dismutase activity were upregulated initially but became downregulated under prolonged water deficit. A total of 104 proteins were found to be differentially accumulated under water stress. The identified proteins were mainly involved in photosynthesis, carbohydrate metabolism, stress defense, energy production, and protein metabolism. Interestingly, substantial incongruence between protein and transcript levels was observed, indicating that gene expression in water-stressed maize seedlings is controlled by complex mechanisms. Finally, we propose a hypothetical model that includes the different molecular, physiological, and biochemical changes that occurred during the response and tolerance of maize seedlings to water deficiency. Our study provides valuable insight for further research into the overall mechanisms underlying drought response and tolerance in maize and other plants.

Silencing barley cystatins HvCPI-2 and HvCPI-4 specifically modifies leaf responses to drought stress

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.

Structural and functional characterization of the triticale (x Triticosecale Wittm.) phytocystatin TrcC-8 and its dimerization-dependent inhibitory activity

Phytocystatins are a group of proteins with significant potential to regulate activities of cysteine proteinases of native and pest/pathogen origins. The two-domain triticale (x Triticosecale Wittm.) phytocystatin TrcC-8 was characterized in this study. This protein belongs to the second group of phytocystatins and contains all the conserved sequences and motifs as well as both N-terminal (CY) and C-terminal (CY-L) domains that are characteristic of phytocystatins with the C-terminal extension. We demonstrated that TrcC-8 forms stable dimers with a significantly reduced inhibitory activity against papain compared to the activity of monomers, indicating the regulatory nature of the oligomerization. Moreover, according to our research, only the N-terminal domain possesses the ability to form dimers, indicating that this part of TrcC-8 is involved in the dimerization of the full-length protein. Homology modelling of TrcC-8 strongly suggests distinct specificities for the CY and CY-L domains, confirmed in experiments with inhibition of the papain. Our results suggest that the CY domain of TrcC-8 may, although markedly weakly and suboptimally, interact with papain in an analogous mode to tarocystatin, while the CY-L domain of TrcC-8 has distinct specificity than tarocystatin.

Analysis of expression and inhibitory activity of a TrcC-6 phytocystatin present in developing and germinating seeds of triticale (×Triticosecale Wittm.)

Storage proteins of cereal seeds are processed during accumulation and degraded during germination primarily by cysteine proteinases. One of the mechanisms controlling the activity of these enzymes is the synthesis of specific inhibitors named phytocystatins. Here we present the complete gene sequence of a triticale ( × Triticosecale Wittm.) phytocystatin, TrcC-6, which encodes a 152-amino acid protein with a putative 25-amino acid signal peptide. This protein has a calculated molecular mass of 16.2 kDa, and was assigned to phylogenetic group B of phytocystatins. Because TrcC-6 transcripts are present in triticale seeds, we hypothesized that this phytocystatin regulates storage protein accumulation and degradation. Therefore, changes in gene expression during the entire period of seed development and germination were examined. TrcC-6 transcripts and TrcC-6 protein levels increased during the maturation of seeds and remained high during the first hours of germination. This enabled us to conclude that TrcC-6 likely regulates seed germination by the regulation of storage protein hydrolysis. For the analysis of TrcC-6 inhibitory activity, recombinant protein was expressed in Escherichia coli BL21 (DE3) and purified. Recombinant TrcC-6 proved to be a potent inhibitor of cysteine proteinases. It inhibited the in vitro activity of papain (EC 3.4.22.2) and ficin (EC 3.4.22.3). Furthermore, native PAGE analysis revealed that recombinant TrcC-6 inhibits the activity of endogenous cysteine proteinases present in germinating seeds of triticale. Based on these results, TrcC-6 is likely one of the important factors that regulate cysteine proteinase activity during the accumulation and mobilization of storage proteins.