Misbah Aslam1, Vincent P M Aparato1, Dae-Yeon Suh2. 1. Department of Chemistry and Biochemistry, University of Regina, Regina, SK, S4S 0A2, Canada. 2. Department of Chemistry and Biochemistry, University of Regina, Regina, SK, S4S 0A2, Canada. suhdaey@uregina.ca.
Abstract
MAIN CONCLUSION: PpORS-produced 2'-oxo-5-pentacosylresorcinol (2'-oxo-C25-RL) restored dehydration tolerance in ors-3, a knockout mutant of PpORS. Feeding experiments with [14C]-2'-oxo-C25-RL suggested the role of PpORS products in cuticular polymer that confer dehydration resistance. 2'-Oxoalkylresorcinol synthase from the moss Physcomitrium (Physcomitrella) patens (PpORS) is the earliest diverged member of plant type III polyketide synthases, and produces very-long-chain 2'-oxoalkylresorcinols in vitro. Targeted knockouts of PpORS (ors) exhibited an abnormal phenotype (increased susceptibility to dehydration), and a defective cuticle in ors was suggested (Li et al., Planta 247:527-541, 2018). In the present study, we investigated chemical rescue of the ors phenotype and also metabolic fates of the PpORS products in the moss. Using C24-CoA as substrate, 2'-oxo-5-pentacosylresorcinol (2'-oxo-C25-RL) and two minor pyrones were first enzymatically prepared as total in vitro products. When a knockout mutant (ors-3) and control strains were grown in the presence of the total in vitro products or purified 2'-oxo-C25-RL, the ability of ors-3 and the control to survive dehydration stress increased in a dose-dependent manner. Structurally analogous long-chain alkylresorcinols also rescued the ors phenotype, although less efficiently. When the moss was grown in the presence of 14C-radiolabeled 2'-oxo-C25-RL, 96% of the radioactivity was recovered only after acid hydrolysis. These findings led us to propose that 2'-oxoalkylresorcinols are the functional in planta products of PpORS and are incorporated into cuticular biopolymers that confer resistance to dehydration. In addition, the earliest diverging ORS clade in phylogenetic trees of plant type III PKSs exclusively comprises bryophyte enzymes that share similar active site substitutions with PpORS. Further studies on these bryophyte enzymes may shed light on their roles in early plant evolution and offer a novel strategy for improving dehydration tolerance in plants.
MAIN CONCLUSION: PpORS-produced 2'-oxo-5-pentacosylresorcinol (2'-oxo-C25-RL) restored dehydration tolerance in ors-3, a knockout mutant of PpORS. Feeding experiments with [14C]-2'-oxo-C25-RL suggested the role of PpORS products in cuticular polymer that confer dehydration resistance. 2'-Oxoalkylresorcinol synthase from the moss Physcomitrium (Physcomitrella) patens (PpORS) is the earliest diverged member of plant type III polyketide synthases, and produces very-long-chain 2'-oxoalkylresorcinols in vitro. Targeted knockouts of PpORS (ors) exhibited an abnormal phenotype (increased susceptibility to dehydration), and a defective cuticle in ors was suggested (Li et al., Planta 247:527-541, 2018). In the present study, we investigated chemical rescue of the ors phenotype and also metabolic fates of the PpORS products in the moss. Using C24-CoA as substrate, 2'-oxo-5-pentacosylresorcinol (2'-oxo-C25-RL) and two minor pyrones were first enzymatically prepared as total in vitro products. When a knockout mutant (ors-3) and control strains were grown in the presence of the total in vitro products or purified 2'-oxo-C25-RL, the ability of ors-3 and the control to survive dehydration stress increased in a dose-dependent manner. Structurally analogous long-chain alkylresorcinols also rescued the ors phenotype, although less efficiently. When the moss was grown in the presence of 14C-radiolabeled 2'-oxo-C25-RL, 96% of the radioactivity was recovered only after acid hydrolysis. These findings led us to propose that 2'-oxoalkylresorcinols are the functional in planta products of PpORS and are incorporated into cuticular biopolymers that confer resistance to dehydration. In addition, the earliest diverging ORS clade in phylogenetic trees of plant type III PKSs exclusively comprises bryophyte enzymes that share similar active site substitutions with PpORS. Further studies on these bryophyte enzymes may shed light on their roles in early plant evolution and offer a novel strategy for improving dehydration tolerance in plants.
Authors: Daniel Cook; Agnes M Rimando; Thomas E Clemente; Joachim Schröder; Franck E Dayan; N P Dhammika Nanayakkara; Zhiqiang Pan; Brice P Noonan; Mark Fishbein; Ikuro Abe; Stephen O Duke; Scott R Baerson Journal: Plant Cell Date: 2010-03-26 Impact factor: 11.277
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