Summary Wood formation is controlled by transcriptional regulatory networks (TRNs) involving regulatory homeostasis determined by combinations of transcription factor (TF)–DNA and TF–TF interactions. Functions of TF–TF interactions in wood formation are still in the early stages of identification. PtrMYB074 is a woody dicot‐specific TF in a TRN for wood formation in Populus trichocarpa. Here, using yeast two‐hybrid and bimolecular fluorescence complementation, we conducted a genome‐wide screening for PtrMYB074 interactors and identified 54 PtrMYB074‐TF pairs. Of these pairs, 53 are novel. We focused on the PtrMYB074‐PtrWRKY19 pair, the most highly expressed and xylem‐specific interactor, and its direct transregulatory target, PtrbHLH186, the xylem‐specific one of the pair's only two direct TF target genes. Using transient and CRISPR‐mediated transgenesis in P. trichocarpa coupled with chromatin immunoprecipitation and electrophoretic mobility shift assays, we demonstrated that PtrMYB074 is recruited by PtrWRKY19 and that the PtrMYB074‐PtrWRKY19 dimers are required to transactive PtrbHLH186. Overexpressing PtrbHLH186 in P. trichocarpa resulted in retarded plant growth, increased guaiacyl lignin, a higher proportion of smaller stem vessels and strong drought‐tolerant phenotypes. Knowledge of the PtrMYB074‐PtrWRKY19‐PtrbHLH186 regulation may help design genetic controls of optimal growth and wood formation to maximize beneficial wood properties while minimizing negative effects on growth.

Post-translational modification of proteins exerts essential roles in many biological processes in plants. The function of these chemical modifications has been extensively characterized in many physiological processes, but how these modifications regulate lignin biosynthesis for wood formation remained largely unknown. Over the past decade, post-translational modification of several proteins has been associated with lignification. Phosphorylation, ubiquitination, glycosylation, and S-nitrosylation of transcription factors, monolignol enzymes, and peroxidases were shown to have primordial roles in the regulation of lignin biosynthesis. The main discoveries of post-translational modifications in lignin biosynthesis are discussed in this review.

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The potential to convert renewable plant biomasses into fuels and chemicals by microbial processes presents an attractive, less environmentally intense alternative to conventional routes based on fossil fuels. This would best be done with microbes that natively deconstruct lignocellulose and concomitantly form industrially relevant products, but these two physiological and metabolic features are rarely and simultaneously observed in nature. Genetic modification of both plant feedstocks and microbes can be used to increase lignocellulose deconstruction capability and generate industrially relevant products. Separate efforts on plants and microbes are ongoing, but these studies lack a focus on optimal, complementary combinations of these disparate biological systems to obtain a convergent technology. Improving genetic tools for plants have given rise to the generation of low-lignin lines that are more readily solubilized by microorganisms. Most focus on the microbiological front has involved thermophilic bacteria from the genera Caldicellulosiruptor and Clostridium, given their capacity to degrade lignocellulose and to form bio-products through metabolic engineering strategies enabled by ever-improving molecular genetics tools. Bioengineering plant properties to better fit the deconstruction capabilities of candidate consolidated bioprocessing microorganisms has potential to achieve the efficient lignocellulose deconstruction needed for industrial relevance.