Abstract
Rehmannia glutinosa production is affected by replanting disease, in which autotoxic harm to plants is mediated by endogenous phenolic acids as allelopathic compounds found in root exudates. These phenolic acids are mostly phenylpropanoid products of plants’ secondary metabolisms. The molecular mechanism of their biosynthesis and release has not been explored in R. glutinosa. P-coumarate-3-hydroxylase (C3H) is the second hydroxylase gene involved in the phenolic acid/phenylpropanoid biosynthesis pathways. C3Hs have been functionally characterized in several plants. However, limited information is available on the C3H gene in R. glutinosa. Here, we identified a putative RgC3H gene and predicted its potential function by in silico analysis and subcellular localization. Overexpression or repression of RgC3H in the transgenic R. glutinosa roots indicated that the gene was involved in allelopathic phenolic biosynthesis. Moreover, we found that these phenolic acid release amount of the transgenic R. glutinosa roots were altered, implying that RgC3H positively promotes their release via the molecular networks of the activated phenolic acid/phenylpropanoid pathways. This study revealed that RgC3H plays roles in the biosynthesis and release of allelopathic phenolic acids in R. glutinosa roots, laying a basis for further clarifying the molecular mechanism of the replanting disease development.
Highlights
R. glutinosa, a species of the Scrophulariaceae family, is a perennial herbaceous plant
Similar to other P450s [15], the sequences included both a heme-iron ligand signature (PFGXGRRXCXG) near the C-terminal, a threonine-containing a binding pocket motif (A/GGXD/ETT/S) for the oxygen molecule required, and a ERR triad (EXXR...R) for catalysis (Figure 1). These results indicated that the RgC3H protein shares the typical characteristics of plant P450 proteins
To experimentally triad (EXXR...R) for catalysis (Figure 1). These results indicated that the RgC3H protein shares the determine the subcellular localization of RgC3H, the complete coding region of the gene was fused to typical characteristics of plant P450 proteins
Summary
R. glutinosa, a species of the Scrophulariaceae family, is a perennial herbaceous plant. Its tuberous roots contain a number of pharmacologically active compounds and are used in traditional Chinese medicine [1,2]. This medicinal plant is affected by replanting disease, in which the continuous monoculture of R. glutinosa leads to serious negative effects on both plant health and the rhizosphere soil, resulting in a marked decline in the biomass and quality of underground tuber roots [3,4,5]. Some endogenous phenolic acids, which are important root exudates, are involved in allelopathy and are prone to directly or indirectly cause autotoxicity, resulting in replanting disease in some plants [6,11,12,13]. Several phenolic acids (e.g., ferulic acid (FA), Plants 2020, 9, 567; doi:10.3390/plants9050567 www.mdpi.com/journal/plants
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