Hartken, D. | Search bioRxiv

bioRxiv2020

Functional requirement of the Arabidopsis importin-α nuclear transport receptor family in autoimmunity mediated by the NLR protein SNC1

IMPORTIN-3/MOS6 (MODIFIER OF SNC1, 6) is one of nine importin- isoforms in Arabidopsis that recruit nuclear localization signal (NLS)-containing cargo proteins to the nuclear import machinery. IMP-3/MOS6 is required genetically for full autoimmunity of the nucleotide-binding leucine-rich repeat (NLR) immune receptor mutant snc1 (suppressor of npr1-1, constitutive 1) and MOS6 also contributes to basal disease resistance. Here, we investigated the contribution of the other importin- genes to both types of immune responses, and we analyzed potential interactions of all importin- isoforms with SNC1. By using reverse-genetic analyses in Arabidopsis and protein-protein interaction assays in N. benthamiana we provide evidence that among the nine -importins in Arabidopsis, IMP-3/MOS6 is the main nuclear transport receptor of SNC1, and that IMP-3/MOS6 is required selectively for autoimmunity of snc1 and basal resistance to mildly virulent Pseudomonas syringae in Arabidopsis. SIGNIFICANCE STATEMENTSpecific requirement for the Arabidopsis -importin MOS6 in snc1-mediated autoimmunity is explained by selective formation of MOS6-SNC1 nuclear import complexes.

plant biology↗

bioRxiv2019

The cell-wall-localised BETA-XYLOSIDASE 4 contributes to immunity of Arabidopsis against Botrytis cinerea

Plant cell walls constitute physical barriers that restrict access of microbial pathogens to the contents of plant cells. The primary cell wall of multicellular plants predominantly consists of cellulose, hemicellulose and pectin. In Arabidopsis, a cell wall-localised protein, BETA-XYLOSIDASE 4 (BXL4) that belongs to a seven-member BETA-XYLOSIDASE (BXL) gene family was induced upon infection with the necrotrophic fungal pathogen Botrytis cinerea and mechanical wounding in a jasmonoyl isoleucine (JA-Ile) dependent manner. Ectopic expression of the BXL4 gene in Arabidopsis seed coat epidermal cells was able to rescue a bxl1 mutant phenotype suggesting that like BXL1, BXL4, had both xylosidase and arabinosidase activity and acts in mura on cell wall polysaccharides. bxl4 mutants show a compromised resistance to B. cinerea. Upon infection, bxl4 mutants accumulated reduced levels of JA-Ile and camalexin. Conditional overexpression of BXL4 resulted in enhanced expression of PDF1.2 and PAD3 transcripts both before and after B. cinerea infection. This was associated with reduced susceptibility of the transgenic lines to B. cinerea. These data suggest that remodelling or degradation of one or more cell wall polysaccharides is important for plant immunity against B. cinerea and plays a role in pathogen-induced JA-Ile and camalexin accumulation. One-sentence summaryBXL4 is a putative bifunctional xylosidase/arabinofuranisodase localising to the apoplast, important for immunity against the necrotrphic pathogen B. cinerea.

plant biology↗