Phytochelatin synthase (PCS, EC 2.3.2.15) is a constitutively expressed cytosolic enzyme, found in a number of prokaryotes and eukaryotes, and amongst plants, preliminarily characterized in charophytes as well as in basal land plants (Degola et al., 2014; Petraglia et al., 2014). At first, PCS was found to be involved in metal detoxification mechanisms (Grill et al., 1989). Nonetheless, the fact that PCS is ubiquitously expressed in the plant clade and in many other organisms, even in the complete absence of toxic metal(loid)s, would lead us to postulate other possible function(s) other than mere metal(loid) detoxification. In fact, PCS appears to be also involved in the catabolism of glutathione-conjugates (Beck et al., 2003), in camalexin production (Su et al., 2011) and in callose formation (Clay et al., 2009). To better understand the functional roles of the enzyme besides metal detoxification, our work was aimed first at delineating Arabidopsis thaliana (At) metabolomics, in control and in Cd-exposed plants (shoots and roots). At this purpose, all metabolites from At wild-type (wt), PCS1 knockout mutant (cad1-3) and PCS-overexpressing mutant (AtPCS1-OE) were compared. First of all, a different accumulation of glutathione (GSH), the substrate of PCS, was detected amongst the three plant lines. Indeed, the evidence of a higher GSH content found in cad1-3 mutants and a minor GSH content in AtPCS1-OE plants, suggests an important role of PCS to maintain GSH homeostasis. Furthermore, an accumulation of 4-methoxy-indol-3-ylmethylglucosinolate was detected in cad1-3 plants grown in the absence/presence of Cd. This glucosinolate is involved in callose production (Clay et al., 2009) and thus could contribute to defense mechanisms against pathogen attacks. Callose staining and pathogen assay experiments in our mutants showed that PCS protects plants against metal toxicity and also contributes to callose deposition; moreover, the PCS expression is essential to the resistance mechanism raised against the bacterium Pseudomonas syringae DC3000. In addition, varying contents of flavonols were found among the three plant lines. An increase of kaempferol was measured in shoots and quercetin in roots of cad1-3 mutants, whilst lower amounts were found in AtPCS1-OE plants, compared with wt. Kaempferol and quercetin play several functions in the plant cell, among which the regulation of auxin efflux. Consequently, the content of indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), indole-3-carboxylic acid (ICA) and indole-3-acetic acid methyl ester (MeIAA) was altered in mutant plants. Not least, different levels of lignin precursors were found among the three plant lines exposed or not to Cd. As expected, stretch experiments proved a difference in terms of force/pressure required for breaking stems of the three plant lines, even grown in control conditions. Therefore, this work has highlighted for the first time potential new roles of AtPCS on cell wall remodeling, metabolism of phenilpropanoids, as well as modulation of auxin in planta distribution.
Effects of phytochelatin synthase on the secondary metabolism of Arabidopsis thaliana plants
Luigi Sanità di Toppi
2017-01-01
Abstract
Phytochelatin synthase (PCS, EC 2.3.2.15) is a constitutively expressed cytosolic enzyme, found in a number of prokaryotes and eukaryotes, and amongst plants, preliminarily characterized in charophytes as well as in basal land plants (Degola et al., 2014; Petraglia et al., 2014). At first, PCS was found to be involved in metal detoxification mechanisms (Grill et al., 1989). Nonetheless, the fact that PCS is ubiquitously expressed in the plant clade and in many other organisms, even in the complete absence of toxic metal(loid)s, would lead us to postulate other possible function(s) other than mere metal(loid) detoxification. In fact, PCS appears to be also involved in the catabolism of glutathione-conjugates (Beck et al., 2003), in camalexin production (Su et al., 2011) and in callose formation (Clay et al., 2009). To better understand the functional roles of the enzyme besides metal detoxification, our work was aimed first at delineating Arabidopsis thaliana (At) metabolomics, in control and in Cd-exposed plants (shoots and roots). At this purpose, all metabolites from At wild-type (wt), PCS1 knockout mutant (cad1-3) and PCS-overexpressing mutant (AtPCS1-OE) were compared. First of all, a different accumulation of glutathione (GSH), the substrate of PCS, was detected amongst the three plant lines. Indeed, the evidence of a higher GSH content found in cad1-3 mutants and a minor GSH content in AtPCS1-OE plants, suggests an important role of PCS to maintain GSH homeostasis. Furthermore, an accumulation of 4-methoxy-indol-3-ylmethylglucosinolate was detected in cad1-3 plants grown in the absence/presence of Cd. This glucosinolate is involved in callose production (Clay et al., 2009) and thus could contribute to defense mechanisms against pathogen attacks. Callose staining and pathogen assay experiments in our mutants showed that PCS protects plants against metal toxicity and also contributes to callose deposition; moreover, the PCS expression is essential to the resistance mechanism raised against the bacterium Pseudomonas syringae DC3000. In addition, varying contents of flavonols were found among the three plant lines. An increase of kaempferol was measured in shoots and quercetin in roots of cad1-3 mutants, whilst lower amounts were found in AtPCS1-OE plants, compared with wt. Kaempferol and quercetin play several functions in the plant cell, among which the regulation of auxin efflux. Consequently, the content of indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), indole-3-carboxylic acid (ICA) and indole-3-acetic acid methyl ester (MeIAA) was altered in mutant plants. Not least, different levels of lignin precursors were found among the three plant lines exposed or not to Cd. As expected, stretch experiments proved a difference in terms of force/pressure required for breaking stems of the three plant lines, even grown in control conditions. Therefore, this work has highlighted for the first time potential new roles of AtPCS on cell wall remodeling, metabolism of phenilpropanoids, as well as modulation of auxin in planta distribution.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
