P5CDH affects the pathways contributing to Pro synthesis after ProDH activation by biotic and abiotic stress conditions

Abstract

Plants facing adverse conditions usually alter proline (Pro) metabolism, generating changes that help restore the cellular homeostasis. These organisms synthesize Pro from glutamate (Glu) or ornithine (Orn) by two-step reactions that share Δ1 pyrroline-5-carboxylate (P5C) as intermediate. In the catabolic process, Pro is converted back to Glu using a different pathway that involves Pro dehydrogenase (ProDH), P5C dehydrogenase (P5CDH), and P5C as intermediate. Little is known about the coordination of the catabolic and biosynthetic routes under stress. To address this issue, we analyzed how P5CDH affects the activation of Pro synthesis, in Arabidopsis tissues that increase ProDH activity by transient exposure to exogenous Pro, or infection with Pseudomonas syringae pv. tomato. Wild-type (Col-0) and p5cdh mutant plants subjected to these treatments were used to monitor the Pro, Glu, and Orn levels, as well as the expression of genes from Pro metabolism. Col-0 and p5cdh tissues consecutively activated ProDH and Pro biosynthetic genes under both conditions. However, they manifested a different coordination between these routes. When external Pro supply was interrupted, wild-type leaves degraded Pro to basal levels at which point Pro synthesis, mainly via Glu, became activated. Under the same condition, p5cdh leaves sustained ProDH induction without reducing the Pro content but rather increasing it, apparently by stimulating the Orn pathway. In response to pathogen infection, both genotypes showed similar trends. While Col-0 plants seemed to induce both Pro biosynthetic routes, p5cdh mutant plants may primarily activate the Orn route. Our study contributes to the functional characterization of P5CDH in biotic and abiotic stress conditions, by revealing its capacity to modulate the fate of P5C, and prevalence of Orn or Glu as Pro precursors in tissues that initially consumed Pro.

Metabolic features of chronic fatigue syndrome

“…Pyrroline-5-carboxylic acid (P5C) was increased in both males and females with CFS (Tables 2 and 3). P5C production is a well-studied response to stress in plants (26) and mammals (27,28). P5C can be produced by the stress-induced oxidation of proline and hydroxyproline from collagen turnover via the enzyme proline oxidase or from glutamate oxidation via P5C synthase (P5CS).…”

Arabidopsis Proline Dehydrogenase Contributes to Flagellin-Mediated PAMP-Triggered Immunity by Affecting RBOHD

“…sqRT-PCR and qRT-PCR were performed as described (Cambiagno et al 2015;Rizzi et al 2015). PCR conditions are indicated in Supplementary Table 1.…”

“…In Arabidopsis, the expression of ProDH can be induced by application of exogenous Pro (Kiyosue et al 1996;Rizzi et al 2015). In fact, Col-0 leaf discs treated with 1 mM Pro accumulated AtProDH1 and AtProDH2 transcripts and ProDH protein within 2 h (Fig.…”

“…Interestingly, preincubation (2 h) of Col-0 samples with T4C or THFA decreased flg22-induced aROS burst in a dose-dependent manner (0.25 to 5.00 mM range). The ability of both compounds to inhibit ProDH throughout this range (Elthon and Stewart 1984;Miller et al 2009;Monteoliva et al 2014;Rizzi et al 2015;Zhu et al 2002) suggests that this enzyme activity is required for full aROS burst. Moreover, 2 mM T4C or 5 mM THFA reduced the aROS to 50% (Supplementary Fig.…”

“…To evaluate if ProDH affects PTI by acting as an enzyme, we assessed the effect of ProDH inhibitors on flg22-mediated aROS burst. The nonreducing Pro analog T4C (thiazolidine-4carboxylate) inhibits Arabidopsis ProDH activity at 1 mM, as determined by consumption of radiolabeled Pro on leaf tissues (Monteoliva et al 2014;Rizzi et al 2015). In turn, THFA (L-tetrahydro-2-furoic acid) exerts this effect in the range of 1 to 5 mM (Krishnan et al 2008;White et al 2007).…”