Response of cell-wall composition and RNA-seq transcriptome to methyl-jasmonate in Brachypodium distachyon callus

Abstract

Main conclusionMethyl-jasmonate induces large increases in p-coumarate linked to arabinoxylan in Brachypodium and in abundance of GT61 and BAHD family transcripts consistent with a role in synthesis of this linkage.Jasmonic acid (JA) signalling is required for many stress responses in plants, inducing large changes in the transcriptome, including up-regulation of transcripts associated with lignification. However, less is known about the response to JA of grass cell walls and the monocot-specific features of arabinoxylan (AX) synthesis and acylation by ferulic acid (FA) and para-coumaric acid (pCA). Here, we show that methyl-jasmonate (MeJA) induces moderate increases in FA monomer, > 50% increases in FA dimers, and five–sixfold increases in pCA ester-linked to cell walls in Brachypodium callus. Direct measurement of arabinose acylated by pCA (Araf-pCA) indicated that most or all the increase in cell-wall pCA was due to pCA ester-linked to AX. Analysis of the RNA-seq transcriptome of the callus response showed that these cell-wall changes were accompanied by up-regulation of members of the GT61 and BAHD gene families implicated in AX decoration and acylation; two BAHD paralogues were among the most up-regulated cell-wall genes (seven and fivefold) after 24 h exposure to MeJA. Similar responses to JA of orthologous BAHD and GT61 transcripts are present in the RiceXPro public expression data set for rice seedlings, showing that they are not specific to Brachypodium or to callus. The large response of AX-pCA to MeJA may, therefore, indicate an important role for this linkage in response of primary cell walls of grasses to JA signalling.Electronic supplementary materialThe online version of this article (10.1007/s00425-018-2968-9) contains supplementary material, which is available to authorized users.

Modification of plant cell walls with hydroxycinnamic acids by BAHD acyltransferases

“…One possibility is that, analogous to the putative role of pCA on lignin discussed below, pCA-GAX may participate in radical transfer, thus catalyzing the oxidative coupling of neighboring FA on GAX. This is compatible with the observation that pCA on GAX rapidly increases in response to jasmonic acid application to Brachypodium callus (Hyde et al, 2018) which could be part of a priming of defense, allowing rapid cross-linking to occur in response to additional signals.…”

Loss of TaIRX9b gene function in wheat decreases chain length and amount of arabinoxylan in grain but increases cross‐linking

“…Since we had previously observed that diferulate (diFA) levels were maintained despite loss of AX in endosperm of RNAi lines (Freeman et al , 2017), we were interested to find a BAHD gene (TaBAHD2A) and a peroxidase gene (TaPRX19D) among the most up‐regulated within endosperm DEGs. BAHD genes in this clade are putatively involved in addition of FA (de Souza et al , 2018) or p ‐coumarate (pCA) to AX (Bartley et al , 2013); we have recently demonstrated that the orthologs of these TaBAHD02 genes are dramatically up‐regulated by methyl‐jasmonate in Brachypodium accompanied by a rise in both FA and pCA linked to AX (Hyde et al , 2018). Tandemly arranged TaBAHD02 paralogues are present on all subgenomes in wheat and were significantly up‐regulated in the endosperm of triple mutants (Figure 5c).…”

“…Therefore, the up‐regulation of BAHD02 and peroxidase genes may be responsible for the increased FA per unit AX and FA dimerization that we observed here (Tables 1 and 3) and previously (Freeman et al , 2017) in response to TaIRX9b repression. Brachypodium orthologues of TaBAHD02 and multiple peroxidases were also substantially up‐regulated following methyl‐jasmonate treatment which also induced increases in cell wall pCA, FA and FA dimerization (Hyde et al , 2018). Here, we obtained evidence that the increased amount of diFA per unit AX resulted in greater cross‐linking between WE‐AX molecules from triples, shown by the much greater decrease in molecular weight induced by saponification (Figure 6c).…”

Assessing the Viability of Recovery of Hydroxycinnamic Acids from Lignocellulosic Biorefinery Alkaline Pretreatment Waste Streams

“…As imilar stress response was observed in Brachypodium distachyon callus grown hydroponically and stimulated with methyl jasmonate, ap lant stress-response hormone. [62] Biomassand APL compositional analysis To determinet he change in lignin-bound pCA,w ea ssayed isolated lignin from the "best" lines by using 2D HSQC NMR spectroscopy (Table S4). The assays showedas trong correlation between the level of PMT expression and the amounto fl igninbound pCA.…”