Abstract
Small or specialized natural products (SNAPs) produced by plants vary greatly in structure and function, leading to selective advantages during evolution. With a limited number of genes available, a high promiscuity of the enzymes involved allows the generation of a broad range of SNAPs in complex metabolic networks. Comparative metabolic studies may help to understand why—or why not—certain SNAPs are produced in plants. Here, we used the wound-induced, vein patterning regulating VEP1 (AtStR1, At4g24220) and its paralogue gene on locus At5g58750 (AtStR2) from Arabidopsis to study this issue. The enzymes encoded by VEP1-like genes were clustered under the term PRISEs (progesterone 5β-reductase/iridoid synthase-like enzymes) as it was previously demonstrated that they are involved in cardenolide and/or iridoid biosynthesis in other plants. In order to further understand the general role of PRISEs and to detect additional more “accidental” roles we herein characterized A. thaliana steroid reductase 1 (AtStR1) and compared it to A. thaliana steroid reductase 2 (AtStR2). We used A. thaliana Col-0 wildtype plants as well as VEP1 knockout mutants and VEP1 knockout mutants overexpressing either AtStR1 or AtStR2 to investigate the effects on vein patterning and on the stress response after treatment with methyl vinyl ketone (MVK). Our results added evidence to the assumption that AtStR1 and AtStR2, as well as PRISEs in general, play specific roles in stress and defense situations and may be responsible for sudden metabolic shifts.
Highlights
Specialized metabolism, sometimes still termed “secondary metabolism”, has been studied extensively in plants and microorganisms
Other than studies related to the metabolism of xenobiotics, comparison of genes, enzymes and metabolites of plants that either do or do not produce a certain group of specialized natural products (SNAPs) provides a new aspect for comparative metabolism
NADPH2 but not NADH2 was accepted as a cosubstrate by A. thaliana steroid reductase 2 (AtStR2) (Table 1)
Summary
Specialized metabolism, sometimes still termed “secondary metabolism”, has been studied extensively in plants and microorganisms. A relaxed substrate specificity of many enzymes enhances a plant’s options to develop complex metabolic grids, because a limited number of genes is available in a plant’s genome to encode the respective enzymes This is the basis for substrate– enzyme coevolution, which has been demonstrated as the fundamental principle leading to the formation of SNAPs [1,2]. Other than studies related to the metabolism of xenobiotics, comparison of genes, enzymes and metabolites of plants that either do or do not produce a certain group of SNAPs provides a new aspect for comparative metabolism This approach may help to understand the more general roles of enzymes assumed to be mainly responsible for the production and accumulation of certain natural compounds
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