Subfunctionalization of Paralog Transcription Factors Contributes to Regulation of Alkaloid Pathway Branch Choice in Catharanthus roseus.

Maite Colinas,Joana G Guedes,Rebecca De Clercq,Fabian Schweizer,Alain Goossens,Jacob Pollier,Dries Vaneechoutte,Klaas Vandepoele,Mariana Sottomayor,Liesbeth De Milde,Deniz G Malat,Francisco J Molina-Hidalgo,Teresa Martínez-Cortés

doi:10.3389/fpls.2021.687406

Abstract

Catharanthus roseus produces a diverse range of specialized metabolites of the monoterpenoid indole alkaloid (MIA) class in a heavily branched pathway. Recent great progress in identification of MIA biosynthesis genes revealed that the different pathway branch genes are expressed in a highly cell type- and organ-specific and stress-dependent manner. This implies a complex control by specific transcription factors (TFs), only partly revealed today. We generated and mined a comprehensive compendium of publicly available C. roseus transcriptome data for MIA pathway branch-specific TFs. Functional analysis was performed through extensive comparative gene expression analysis and profiling of over 40 MIA metabolites in the C. roseus flower petal expression system. We identified additional members of the known BIS and ORCA regulators. Further detailed study of the ORCA TFs suggests subfunctionalization of ORCA paralogs in terms of target gene-specific regulation and synergistic activity with the central jasmonate response regulator MYC2. Moreover, we identified specific amino acid residues within the ORCA DNA-binding domains that contribute to the differential regulation of some MIA pathway branches. Our results advance our understanding of TF paralog specificity for which, despite the common occurrence of closely related paralogs in many species, comparative studies are scarce.

Highlights

Plant specialized metabolites are chemically diverse, typically species- or taxa-specific and have often evolved in adaptation to the ecological niche of the plant
We further selected those transcription factors (TFs) that showed coexpression with (i) multiple pathway genes and (ii) monoterpenoid indole alkaloid (MIA) pathway genes for which till no transcriptional regulators are known, in particular genes belonging to the stemmadenine or vindoline branches or involved in catharanthine biosynthesis, and that were not predicted to act as repressors
While C. roseus is traditionally known as a medicinal plant, it is increasingly being established as a model species for plant specialized metabolism in general

Summary

Introduction

Plant specialized metabolites are chemically diverse, typically species- or taxa-specific and have often evolved in adaptation to the ecological niche of the plant. Within the plant, their production often exclusively takes place in specific organs or cell types and may be up-regulated precisely in response to defined environmental conditions [for a review, see Colinas and Goossens (2018)]. The medicinal plant Catharanthus roseus is well-known as being the only source of the important anti-cancer compounds vinblastine and vincristine (Van Der Heijden et al, 2004) These complex molecules belong to the class of monoterpenoid indole alkaloids (MIAs); around 150 different MIAs are estimated to occur in C. roseus (Van Der Heijden et al, 2004). The identification of many of the involved biosynthetic enzymes has revealed that genes involved in the different MIA pathway steps and branches are expressed in a cell type-specific, organspecific and stress-dependent manner, making this species an ideal model to study how a modular system of different TFs possibly regulates specialized metabolism (Courdavault et al, 2014; Dugé De Bernonville et al, 2015)

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