Integrative multi-omic analysis identifies genes associated with cuticular wax biogenesis in adult maize leaves.

Studying the genetic basis of leaf wax composition and its correlation with leaf cuticular conductance (gc) is crucial for improving crop productivity. The leaf cuticle, which comprises a cutin matrix and various waxes, functions as an extracellular hydrophobic layer, protecting against water loss upon stomatal closure. To address the limited understanding of genes associated with the natural variation of adult leaf cuticular waxes and their connection to gc, we conducted statistical genetic analyses using leaf transcriptomic, metabolomic, and physiological data sets collected from a maize (Zea mays L.) panel of ∼300 inbred lines. Through a random forest analysis with 60 cuticular wax traits, it was shown that high molecular weight wax esters play an important role in predicting gc. Integrating results from genome-wide and transcriptome-wide studies (GWAS and TWAS) via a Fisher's combined test revealed 231 candidate genes detected by all three association tests. Among these, 11 genes exhibit known or predicted roles in cuticle-related processes. Throughout the genome, multiple hotspots consisting of GWAS signals for several traits from one or more wax classes were discovered, identifying four additional plausible candidate genes and providing insights into the genetic basis of correlated wax traits. Establishing a partially shared genetic architecture, we identified 35 genes for both gc and at least one wax trait, with four considered plausible candidates. Our study enhances the understanding of how adult leaf cuticle wax composition relates to gc and implicates both known and novel candidate genes as potential targets for optimizing productivity in maize.

ß-Glucan-binding proteins are key modulators of immunity and symbiosis in mutualistic plant-microbe interactions.

In order to discriminate between detrimental, commensal, and beneficial microbes, plants rely on polysaccharides such as ß-glucans, which are integral components of microbial and plant cell walls. The conversion of cell wall-associated ß-glucan polymers into a specific outcome that affects plant-microbe interactions is mediated by hydrolytic and non-hydrolytic ß-glucan-binding proteins. These proteins play crucial roles during microbial colonization: they influence the composition and resilience of host and microbial cell walls, regulate the homeostasis of apoplastic concentrations of ß-glucan oligomers, and mediate ß-glucan perception and signaling. This review outlines the dual roles of ß-glucans and their binding proteins in plant immunity and symbiosis, highlighting recent discoveries on the role of ß-glucan-binding proteins as modulators of immunity and as symbiosis receptors involved in the fine-tuning of microbial accommodation.

Strigolactone deficiency induces jasmonate, sugar and flavonoid phytoalexin accumulation enhancing rice defense against the blast fungus Pyricularia oryzae.

Strigolactones (SLs) are carotenoid-derived phytohormones that regulate plant growth and development. While root-secreted SLs are well-known to facilitate plant symbiosis with beneficial microbes, the role of SLs in plant interactions with pathogenic microbes remains largely unexplored. Using genetic and biochemical approaches, we demonstrate a negative role of SLs in rice (Oryza sativa) defense against the blast fungus Pyricularia oryzae (syn. Magnaporthe oryzae). We found that SL biosynthesis and perception mutants, and wild-type (WT) plants after chemical inhibition of SLs, were less susceptible to P. oryzae. Strigolactone deficiency also resulted in a higher accumulation of jasmonates, soluble sugars and flavonoid phytoalexins in rice leaves. Likewise, in response to P. oryzae infection, SL signaling was downregulated, while jasmonate and sugar content increased markedly. The jar1 mutant unable to synthesize jasmonoyl-l-isoleucine, and the coi1-18 RNAi line perturbed in jasmonate signaling, both accumulated lower levels of sugars. However, when WT seedlings were sprayed with glucose or sucrose, jasmonate accumulation increased, suggesting a reciprocal positive interplay between jasmonates and sugars. Finally, we showed that functional jasmonate signaling is necessary for SL deficiency to induce rice defense against P. oryzae. We conclude that a reduction in rice SL content reduces P. oryzae susceptibility by activating jasmonate and sugar signaling pathways, and flavonoid phytoalexin accumulation.

A GH81-type ß-glucan-binding protein enhances colonization by mutualistic fungi in barley.

Cell walls are important interfaces of plant-fungal interactions, acting as robust physical and chemical barriers against invaders. Upon fungal colonization, plants deposit phenolics and callose at the sites of fungal penetration to prevent further fungal progression. Alterations in the composition of plant cell walls significantly impact host susceptibility. Furthermore, plants and fungi secrete glycan hydrolases acting on each other's cell walls. These enzymes release various sugar oligomers into the apoplast, some of which activate host immunity via surface receptors. Recent characterization of cell walls from plant-colonizing fungi has emphasized the abundance of ß-glucans in different cell wall layers, which makes them suitable targets for recognition. To characterize host components involved in immunity against fungi, we performed a protein pull-down with the biotinylated ß-glucan laminarin. Thereby, we identified a plant glycoside hydrolase family 81-type glucan-binding protein (GBP) as a ß-glucan interactor. Mutation of GBP1 and its only paralog, GBP2, in barley led to decreased colonization by the beneficial root endophytes Serendipita indica and S. vermifera, as well as the arbuscular mycorrhizal fungus Rhizophagus irregularis. The reduction of colonization was accompanied by enhanced responses at the host cell wall, including an extension of callose-containing cell wall appositions. Moreover, GBP mutation in barley also reduced fungal biomass in roots by the hemibiotrophic pathogen Bipolaris sorokiniana and inhibited the penetration success of the obligate biotrophic leaf pathogen Blumeria hordei. These results indicate that GBP1 is involved in the establishment of symbiotic associations with beneficial fungi-a role that has potentially been appropriated by barley-adapted pathogens.