Biology subjects

Nour-Eldin, H. H.

Publications and source records attributed to Nour-Eldin, H. H..

9 recordsLinked to original sources

bioRxiv2026

Water stress adaptive responses in plants require movement of ABA and AB-aldehyde from vascular to target tissues

Vascular plants rapidly coordinate root and shoot responses to water stress. Abscisic acid (ABA) mediates these adaptations; however, it remains unclear which cells produce ABA, whether ABA synthesis shifts during stress, and whether ABA movement is required for its adaptive functions. Here, we map ABA biosynthesis at cellular resolution in Arabidopsis and report that water-stress adaptive responses in roots and shoots require movement of ABA and its precursor AB-aldehyde from vascular tissues to target cells. We suggest that ABA accumulation arises from two parallel routes: (i) ABA synthesized in the vasculature via ABA2 and AAO3, then moving to guard cells, and (ii) phloem-derived AB-aldehyde being converted to ABA in the epidermis or bundle sheath by AAO1 and AAO2. Finally, we predict that tightly packed cells beneath leaf veins facilitate efficient ABA delivery to guard cells, an anatomical arrangement that has enabled angiosperms to evolve the use of ABA to rapidly close stomata.

plant biology↗

bioRxiv2025

Proline transporters balance the salicylic acid-mediated trade-off between regeneration and immunity in plants

A robust immune response and regenerative capacity are both essential for survival after injury. In plants, salicylic acid (SA) is essential for activating immunity but simultaneously suppresses regenerative capacity. The mechanisms coordinating the trade-off between immunity and regeneration remain poorly understood. Here, we identify proline transporters as key regulators of this balance. Mutations in two wound-induced proline transporters, ProT2 and ProT3, rescued exogenous proline-induced suppression of de novo root regeneration (DNRR) and enhanced DNRR. ProTs are required for SA-mediated suppression of regeneration, without affecting SA-dependent defense responses. Mechanistically, a ProT3-CPK1 complex modulates the dynamics of wound-induced reactive oxygen species (ROS), sustaining a ROS level that restricts DNRR after wounding. Notably, pharmacological inhibition of proline transport rescued SA-mediated suppression of regeneration and enhanced regeneration across multiple plant species. These findings establish proline transporter as a regulatory hub integrating stress-induced proline metabolism, SA signaling, and ROS homeostasis to balance immunity and regeneration, and highlight chemical inhibition of proline transport as a strategy to improve crop regeneration under biotic stresses without compromising disease resistance.

plant biology↗

bioRxiv2025

A versatile method to expand and compare transporter substrate spectra

Membrane transport proteins (transporters) are critical players in the physiology of complex organisms. The range of metabolites a transporter translocates across a membrane (substrate spectra) determines the membrane selectivity and, consequently, the transporters physiologic function. Nevertheless, determining the full substrate spectra of a transporter, and hence its role(s) in the organism, remains a daunting challenge. Many transporters lack an experimentally determined substrate, and many show a puzzling substrate promiscuity. Substrate promiscuity raises questions about which experimentally defined substrates are physiologic, which are not, and which are missing. Targeted approaches to determine transporter substrate spectra present limitations: Compound availability, lack of unexpected cofactors, and the researchers biases. To tackle these issues, transporters can be screened with complex native metabolites to generate new hypotheses on their function. Here, we describe an untargeted method to expand and compare the substrate spectra of sets of plant transporters. This method compares the substrate spectra of different transporters when expressed in Xenopus laevis oocytes and exposed to plant metabolic extracts. Comparing the transport-mediated accumulation of metabolites enables us to contextualize the relative transporter activity towards the same set of metabolites from undefined mixtures. Additionally, metabolite accumulation patterns across transporter sets allow us to annotate novel compounds. We validate the method with three well-characterized transporters, where we find unreported substrate spectra specificities and detect the transport of tens of metabolites at a time. We screen a set of fourteen transporters and find unreported activities for eight of them, some of which are confirmed from pure compounds. Finally, we propose to reinterpret the role of two plant transporters previously linked to developmental regulation (phytohormone transport) in light of their substrate promiscuity.

molecular biology↗

bioRxiv2023

The aerial epidermis is a major site of quinolizidine alkaloid biosynthesis in narrow-leafed lupin

Lupins are promising legume crops that accumulate toxic alkaloids in the seeds, complicating their use as high-protein crops. The alkaloids are synthesized in green organs (leaves, stems, and pods) and a subset of them is transported to the seeds during fruit development. The exact sites of biosynthesis and accumulation remain unknown, however mesophyll cells have been proposed as sources, and epidermal cells have been suggested as sinks. We examined the spatial localization of the alkaloids in biosynthetic organs of narrow-leafed lupin using mass spectrometry-based imaging (MSI). The alkaloids that accumulate in seeds ("core" alkaloids) were evenly distributed across tissues, however their esterified versions accumulated primarily in the epidermis. In addition, we generated a tissue-specific RNAseq dataset of biosynthetic organs using laser-capture microdissection. The dataset revealed that alkaloid biosynthetic genes are strongly expressed in the epidermis. To confirm the biosynthetic capacity of the leaf epidermis, we combined precursor feeding studies with mass spectrometry imaging, which showed that the lower epidermis is highly biosynthetic. Our work challenges the current assumptions on the precise sites of lupin alkaloid biosynthesis, with direct implications for the elucidation of the alkaloid biosynthesis pathway and the long-distance transport network from source to seed.

plant biology↗

bioRxiv2023

Mechanistic insight into substrate specificity of plant glucosinolate transporters

Plants depend on transport processes for correct allocation of specialized metabolites. This is important for optimal defense, avoidance of autotoxicity, connecting compartmented biosynthetic modules and more. Transport of a wide variety of specialized metabolites is mediated by transporters from the Nitrate and Peptide transporter Family (NPF), which belongs to the Major Facilitator Superfamily (MFS). However, the mechanism by which NPF members recognize and transport specialized metabolites remains unknown. Here we mutate eight residues to reciprocally swap the substrate-preference of two closely related glucosinolate transporters (GTRs). Seven of these residues assemble in a ring-like structure in all conformations of the transporters. We labeled the ring-like structure a selectivity filter and based on docking studies, we propose that the interaction between the selectivity filter and the glucosinolate side chain determines whether a given glucosinolate is recognized as a substrate. Besides partly explaining the distinct substrate preference of GTR1 (NPF2.10) and GTR3 (NPF2.9), this study proposes fundamental principles of substrate recognition in the NPF and establishes the GTR subclade as a novel model system for studying structure function relationships in the NPF.

molecular biology↗

bioRxiv2021

ABA homeostasis and long-distance translocation is redundantly regulated by ABCG ABA importers

The effects of abscisic acid (ABA) on plant growth, development and response to the environment depend on local ABA concentrations. Here, we exploited a genome-scale amiRNA screen, targeting the Arabidopsis transportome, to show that ABA homeostasis is regulated by two previously unknown ABA transporters. ABCG17 and ABCG18 are localized to the plasma membranes of leaf mesophyll and stem cortex cells to redundantly promote ABA import, leading to conjugated inactive ABA sinks, thus restricting stomatal closure. ABCG17 and ABCG18 double knockdown revealed that the transporters encoded by these genes not only limit stomatal aperture size, conductance and transpiration while increasing water-use efficiency but also control ABA translocation from the shoot to the root to regulate lateral root emergence. The proposed ABCG17- and ABCG18-dependent ABA glucosyl ester shoot sink mechanism is restrained under abiotic stress conditions to further activate the ABA responses.

plant biology↗

bioRxiv2021

Sugar transporters enable a leaf beetle to accumulate plant defense compounds

Many herbivorous insects selectively accumulate plant toxins for defense against predators; however, little is known about the transport processes that enable insects to absorb and store defense compounds in the body. Here, we investigate how a specialist herbivore, the horseradish flea beetle, accumulates high amounts of glucosinolate defense compounds in the hemolymph. Using phylogenetic analyses of coleopteran membrane transporters of the major facilitator superfamily, we identified a clade of glucosinolate-specific transporters (PaGTRs) belonging to the sugar porter family. PaGTR expression was predominantly detected in the excretory system, the Malpighian tubules. Silencing of PaGTRs led to elevated glucosinolate excretion, significantly reducing the levels of sequestered glucosinolates in beetles. This suggests that PaGTRs reabsorb glucosinolates from the Malpighian tubule lumen to prevent their loss by excretion. Ramsay assays performed with dissected Malpighian tubules confirmed a selective retention of glucosinolates. Thus, the selective accumulation of plant defense compounds in herbivorous insects can depend on the ability to prevent excretion.

physiology↗

bioRxiv2020

Identification and characterization of phlorizin transporter from Arabidopsis thaliana and its application for phlorizin production in Saccharomyces cerevisiae

Bioengineering aimed at producing complex and valuable plant specialized metabolites in microbial hosts requires efficient uptake of precursor molecules and export of final products to alleviate toxicity and feedback inhibition. Plant genomes encode a vast repository of transporters of specialized metabolites that-- due to lack of molecular knowledge--remains largely unexplored in bioengineering. Using phlorizin as a case study--an anti-diabetic and anti-cancerous flavonoid from apple--we demonstrate that brute-force functional screening of plant transporter libraries in Xenopus oocytes is a viable approach to identify transporters for bioengineering. By screening 600 Arabidopsis transporters, we identified and characterized purine permease 8 (AtPUP8) as a bidirectional phlorizin transporter. Functional expression in the plasma membrane of a phlorizin-producing yeast strain increased phlorizin titer by more than 80 %. This study provides a generic approach for identifying plant exporters of specialized metabolites and demonstrates the potential of transport-engineering for improving yield in bioengineering approaches.

molecular biology↗

bioRxiv2019

An Optimized Screen Reduces the Number of GA Transporters and provides Insights into NPF Substrate Determinants

Based on recent in vitro data, a relatively large number of the plant Nitrate transporter 1/Peptide transporter Family (NPF) proteins has been suggested to function as gibberellic acid (GA) transporters. Most GA transporting NPF proteins also appear to transport other structurally unrelated phytohormones or metabolites. Several of the GAs used in previous in vitro assays are membrane permeable weak organic acids whose movement across membranes are influenced by the pH-sensitive ion-trap mechanism. Moreover, a large proportion of in vitro GA transport activities have been demonstrated indirectly via long-term yeast-based GA-dependent growth assays that are limited to detecting transport of bioactive GAs. Thus, there is a need for an optimized transport assay for identifying and characterizing GA transport. Here, we develop an improved transport assay in Xenopus laevis oocytes wherein we directly measure movement of six different GAs across oocyte membranes over short time. We show that membrane permeability of GAs in oocytes can be predicted based on number of oxygen atoms and that several GAs do not diffuse over membranes regardless of changes in pH values. In addition, we show that small changes in internal cellular pH can result in strongly altered distribution of membrane permeable phytohormones. This prompts caution when interpreting heterologous transport activities. We use our transport assay to screen all Arabidopsis thaliana NPF proteins for transport activity towards six GAs (two membrane permeable and four non-permeable). The results presented here, significantly reduce the number of bona fide NPF GA transporters in Arabidopsis and narrow the activity to fewer subclades within the family. Furthermore, to gain first insight into the molecular determinants of substrate specificities towards organic molecules transported in the NPF, we charted all surface exposed amino acid residues in the substrate-binding cavity and correlated them to GA transport. This analysis identified distinct residues within the substrate-binding cavity that are shared between GA transporting NPF proteins; the potential roles of these residues in determining substrate specificity are discussed.

biochemistry↗