Reinstaedler, A. | bioRxiv Science

bioRxiv2022

Interplay of EXO70 and MLO proteins modulates trichome cell wall composition and powdery mildew susceptibility

EXO70 proteins are essential constituents of the octameric exocyst complex implicated in vesicle tethering during exocytosis, while MLO proteins are plant-specific calcium channels of which some isoforms play a key role during fungal powdery mildew pathogenesis. We here detected by a variety of histochemical staining procedures an unexpected phenotypic overlap of A. thaliana exo70H4 and mlo2 mlo6 mlo12 triple mutant plants regarding the biogenesis of leaf trichome secondary cell walls. Biochemical and Fourier transform infrared spectroscopic analyses of isolated trichomes corroborated deficiencies in the composition of trichome cell walls in exo70H4 and mlo2 mlo6 mlo12 mutants. Transgenic lines expressing fluorophore- tagged EXO70H4 and MLO variants exhibited extensive co-localization of these proteins at the trichome plasma membrane and cell wall. Furthermore, mCherry- EXO70H4 mislocalized in trichomes of the mlo triple mutant and, vice versa, MLO6- GFP exhibited aberrant subcellular localization in trichomes of the exo70H4 mutant. Transgenic expression of GFP-marked PMR4 callose synthase, a previously identified cargo of EXO70H4 dependent exocytosis, revealed reduced cell wall delivery of GFP- PMR4 in mlo triple mutant plants. In vivo protein-protein interaction assays uncovered isoform-preferential physical interaction between EXO70 and MLO proteins. Finally, exo70H4 and mlo mutants, when combined, showed synergistically enhanced resistance to powdery mildew attack. Taken together, our data point to an isoform- specific interplay of EXO70 and MLO proteins in the modulation of trichome cell wall biogenesis and powdery mildew susceptibility, possibly by (co-)regulating focal secretion of cell wall-related cargo.

plant biology↗

bioRxiv2021

A fungal powdery mildew pathogen induces extensive local and marginal systemic changes in the Arabidopsis thaliana microbiota

O_LIPowdery mildew is a foliar disease caused by epiphytically growing obligate biotrophic ascomycete fungi. How powdery mildew colonization affects host resident microbial communities locally and systemically remains poorly explored. C_LIO_LIWe performed powdery mildew (Golovinomyces orontii) infection experiments with Arabidopsis thaliana grown in either natural soil or a gnotobiotic system and studied the influence of pathogen invasion into standing natural multi-kingdom or synthetic bacterial communities (SynComs). C_LIO_LIWe found that after infection of soil-grown plants, G. orontii outcompetes numerous resident leaf-associated fungi. We further detected a significant shift in foliar but not root-associated bacterial communities in this setup. Pre-colonization of germ-free A. thaliana leaves with a bacterial leaf-SynCom, followed by G. orontii invasion, induced an overall similar shift in the foliar bacterial microbiota and minor changes in the root-associated bacterial assemblage. However, a standing root SynCom in root samples remained robust against foliar infection with G. orontii. Although pathogen growth was unaffected by the leaf SynCom, fungal infection caused a more than two-fold increase in leaf bacterial load. C_LIO_LIOur findings indicate that G. orontii infection affects mainly microbial communities in local plant tissue, possibly driven by pathogen-induced changes in source-sink relationships and host immune status. C_LI

plant biology↗