Subgroup 4 R2R3-MYBs in conifer trees: gene family expansion and contribution to the isoprenoid- and flavonoid-oriented responses

Abstract

Transcription factors play a fundamental role in plants by orchestrating temporal and spatial gene expression in response to environmental stimuli. Several R2R3-MYB genes of the Arabidopsis subgroup 4 (Sg4) share a C-terminal EAR motif signature recently linked to stress response in angiosperm plants. It is reported here that nearly all Sg4 MYB genes in the conifer trees Picea glauca (white spruce) and Pinus taeda (loblolly pine) form a monophyletic clade (Sg4C) that expanded following the split of gymnosperm and angiosperm lineages. Deeper sequencing in P. glauca identified 10 distinct Sg4C sequences, indicating over-represention of Sg4 sequences compared with angiosperms such as Arabidopsis, Oryza, Vitis, and Populus. The Sg4C MYBs share the EAR motif core. Many of them had stress-responsive transcript profiles after wounding, jasmonic acid (JA) treatment, or exposure to cold in P. glauca and P. taeda, with MYB14 transcripts accumulating most strongly and rapidly. Functional characterization was initiated by expressing the P. taeda MYB14 (PtMYB14) gene in transgenic P. glauca plantlets with a tissue-preferential promoter (cinnamyl alcohol dehydrogenase) and a ubiquitous gene promoter (ubiquitin). Histological, metabolite, and transcript (microarray and targeted quantitiative real-time PCR) analyses of PtMYB14 transgenics, coupled with mechanical wounding and JA application experiments on wild-type plantlets, allowed identification of PtMYB14 as a putative regulator of an isoprenoid-oriented response that leads to the accumulation of sesquiterpene in conifers. Data further suggested that PtMYB14 may contribute to a broad defence response implicating flavonoids. This study also addresses the potential involvement of closely related Sg4C sequences in stress responses and plant evolution.

The Flavonoid Biosynthetic Enzyme Chalcone Isomerase Modulates Terpenoid Production in Glandular Trichomes of Tomato

“…diurnal) cues (Dudareva et al, 2000(Dudareva et al, , 2003. More intriguingly, recent transgenic studies provide evidence for the existence of transcription factors that promote metabolic flux through both pathways (Bedon et al, 2010;Ben Zvi et al, 2012). Our characterization of pleiotropic metabolic defects in the tomato af mutant is consistent with the emerging role of secondary metabolites as lineage-specific signals that coordinate responses to changing environments (Clay et al, 2009;Jander and Clay, 2011;Xiao et al, 2013).…”

“…For example, dimethyl allyl diphosphate is used for the synthesis of prenylated flavonoids and other terpenophenolics in glandular trichomes of some plant species (Nagel et al, 2008;Wang et al, 2008;Shen et al, 2012;Voo et al, 2012). There is also evidence that members of the MYB family of transcription factors play a role in coordinating metabolic activity between the flavonoid and terpenoid biosynthetic pathways (Bedon et al, 2010;Ben Zvi et al, 2012).…”

A White Spruce Gene Catalog for Conifer Genome Analyses

“…Given that their radiation largely predates that of flowering plants and their apparent slow rate of morphological evolution (Gernandt et al, 2011) and their conserved genome macrostructure , it stands to reason that gymnosperms may have fewer TFs in their genomes than angiosperms. Conifers were previously shown to have fewer members overall and to lack members in specific subfamilies for TF families such as Knox I and HD-Zip-III and to have more numerous recent gene duplications in closely related subfamilies (Guillet-Claude et al, 2004;Cô té et al, 2010) and in R2R3-MYBs (Bedon et al, 2010), among others. Consistent with the model presented by Lang and colleagues (2010), the occurrence and distribution of TF protein domains in the cDNA resource described here strongly suggest that lower overall representation applies to the majority of TF families (Fig.…”

Terpene Down-Regulation Triggers Defense Responses in Transgenic Orange Leading to Resistance against Fungal Pathogens

“…Using intact mature flavedo tissue, gene expression in the AS3 and AS7 lines was compared with that of two independent EV control lines. The ectopic up-regulation or down-regulation of genes involved in eliciting defense responses against herbivores and plant pests usually results in phenotypic aberrations, because such genes are also important for growth and development (Bedon et al, 2010;Kallenbach et al, 2010;Yang et al, 2012). As AS orange plants and fruits were visually indistinguishable from EV controls, we hypothesized that the impact of D-limonene synthase down-regulation on the general transcript profile would not be very high quantitatively.…”

“…5B; Table I; Supplemental Table S2). Most of these TFs have been related to the elicitation of secondary metabolism and defense (Bedon et al, 2010;De Geyter et al, 2012).…”