Biology subjects

El-Azaz, J.

Publications and source records attributed to El-Azaz, J..

4 recordsLinked to original sources

bioRxiv2026

Establishment of the grass lignin metabolic network during monocot evolution

Plants produce a vast diversity of chemical compounds, yet the evolutionary history of the underlying complex metabolic networks remains poorly understood. Grasses (Poaceae family) possess a unique lignin metabolic network that can utilize both phenylalanine and tyrosine as precursors to synthesize canonical lignin as well as non-canonical acylated and tricin-conjugated lignin subunits. This study traces the evolutionary remodeling and establishment of the grass lignin metabolic network by combining phylogenomics with biochemical and chemical analyses across Poaceae, Poales, and other monocot species. These multidisciplinary comparative analyses reveal that the acylated lignin evolved in commelinids, followed by tyrosine-derived lignin biosynthesis in non-grass graminids through fine-tuning of pathway enzymes and transcriptional factors. Later, biosynthesis and incorporation of the flavonoid tricin into the cell wall took place within the core grasses via the evolution of chrysoeriol 5'-hydroxylase (C5'H) activity within the CYP75B enzyme family. These findings illustrate the emergence of different network modules at distinct times during monocot evolution that became integrated into the complex yet coherent metabolic network underlying the unique lignin chemical diversity of grasses.

plant biology↗

bioRxiv2026

AATRhg1 is a tonoplast protein that alters amino acid, metabolic and defense responses and nematode resistance

Soybean cyst nematode (SCN, Heterodera glycines) causes significant soybean yield losses. The Rhg1 locus is a major contributor to SCN resistance and contains three genes that mediate this trait including Rhg1-GmAAT (Glyma.18G022400), which encodes putative amino acid transporter AATRhg1. The molecular function of AATRhg1 in SCN resistance is not understood. In this study, rhg1-b soybean lines with Rhg1-GmAAT silencing demonstrated that Rhg1-GmAAT can contribute resistance against HG 0 SCN and also against problematic HG 2.5.7 populations that partially overcome rhg1-b-mediated resistance. An AATRhg1 Y268L mutant complemented SCN resistance in Rhg1-GmAAT-silenced plants while an AATRhg1 D122A mutant did not. Overexpression of Rhg1-GmAAT was not sufficient to enhance SCN resistance, suggesting that AATRhg1 requires coordinated activity with other proteins or pathways. Confocal microscopy demonstrated that AATRhg1 localizes to the tonoplast in soybean root cells. Amino acid, transcriptomic and metabolomic profiles were determined for SCN-infected root segments 3 days after SCN inoculation. In Rhg1-GmAAT-silenced plants relative to fully resistant (non-silenced) rhg1-b plants, levels of leucine, isoleucine, and tyrosine were significantly elevated. Rhg1-GmAAT silencing reduced SCN-responsive transcript abundances for multiple processes, significantly including genes for MAPK signaling, ethylene responses and starch and sucrose metabolism. The most common identified metabolomic changes were in amino acid derivatives, shikimate/phenylpropanoid/isoflavonoid compounds, terpenoids, and especially fatty acids. These findings can guide further investigation into the mechanisms by which AATRhg1 contributes to SCN resistance.

plant biology↗

bioRxiv2025

Dynamic Retuning of Precursor Supply Before and After the Evolution of the Dual Lignin Pathway in Poales

ABSTRACTPlants produce diverse and abundant natural products, critical for plant adaptation and human society. While tremendous diversification of plant natural product pathways is well documented, how the upstream primary metabolism evolved in coordination with the lineage-specific pathways remain poorly understood. Here we studied the evolution of aromatic amino acid (AAA) biosynthesis during the emergence of tyrosine-derived lignin pathway uniquely found in grasses and closely related Poales. Phylogeny-guided in vitro and in planta functional analyses were conducted on two key regulatory enzymes--3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DHS) and arogenate dehydrogenase (TyrA)--catalyzing the first and last steps of AAA and tyrosine biosynthesis, respectively. Deregulated TyrAs were broadly present across Poales, with PACMAD grasses exhibiting stronger deregulation, suggesting that the active tyrosine biosynthesis likely emerged before, but were also selected upon, the evolution of tyrosine-lignin pathway. Conversely, DHS deregulation occurred more recently within BOP grasses after the emergence of tyrosine-lignin pathway, via multiple mutations that acted synergistically in the enzymes allosteric regulatory domain. The study highlights how the regulation of upstream primary metabolism is dynamically tuned both before and after the evolution of emerging natural product pathways. These findings underscore the importance of coordinating primary and secondary metabolism for efficient production of natural products in plants.

plant biology↗

bioRxiv2019

Allosteric deregulation of phenylalanine biosynthesis evolved with the emergence of vascular plants

Phenylalanine (Phe) is the precursor of essential secondary products in plants. Here we show that a key, rate-limiting step in Phe biosynthesis, which is catalyzed by arogenate dehydratase (ADT), experienced allosteric de-regulation during evolution. Enzymes from microorganisms and type-I ADTs from plants are strongly feedback-inhibited by Phe, while type-II isoforms remain active at high levels of Phe. We have found that type-II ADTs are widespread across seed plants and their overproduction resulted in a dramatic accumulation of Phe in planta, up to 40-times higher than those observed following the expression of type-I enzymes. Punctual changes in the allosteric binding site of Phe and adjacent region are responsible for the observed relaxed regulation. The phylogeny of plant ADTs evidences that the emergence of type-II isoforms with relaxed regulation occurred at some point in the transition between non-vascular plants and tracheophytes enabling the massive production of Phe-derived compounds, primarily lignin, which are attributes of vascular plants.

plant biology↗