Polygalacturonase gene FaPG1 downregulation is related to increased strawberry fruit resistance to fungal decay

Plant health is a major target in breading programs because crops are under constant biotic stress, and climate change is exacerbating pests and disease negative impacts in agriculture. Obtaining crop varieties armed with better defences is a potential strategy to reduce losses from biotic attacks. Plant cell walls perform crucial roles on many physiological processes, and under biotic stress, play crucial defensive roles as protecting barrier, as well as a source of integrity signalling molecules. Plant immunity has evolved a complex multi-layered system which first line of defence is initiated by conserved molecular patterns coming from pathogens, named pathogen-associated molecular patterns or PAMPs, or from their own corrupted cell walls due to pathogen invasion, named damaged-associated molecular patterns or DAMPs. Accumulating evidence from cell wall mutants has unveiled several components and mechanisms of plant innate immunity under biotic stresses, mostly in Arabidopsis, but still little is known from species with agronomic interest as strawberry. Our group has an established strawberry transgenic collection of cell wall mutants. Among them, RNAseq expression profiles of FaPG1 mutants has shown downregulation of other cell wall related genes than PG [1], but the mechanisms underneath required further investigation. FaPG genes code for enzymes with endo-PG activity related to oligogalacturonic acid (OGA) release, which would be associated to the changes in gene expression of other cell wall genes than FaPG. In this work, postharvest assays of FaPG1 fruits showed not only the increased fruit firmness typical of this mutant, but a better resistance to fungal infections by Botrytis cinerea, enhancing fruit shelf life in comparison with control fruits.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE 1 (ADPG1) releases latent defense signals in stems with reduced lignin content

There is considerable interest in engineering plant cell wall components, particularly lignin, to improve forage quality and biomass properties for processing to fuels and bioproducts. However, modifying lignin content and/or composition in transgenic plants through down-regulation of lignin biosynthetic enzymes can induce expression of defense response genes in the absence of biotic or abiotic stress. Arabidopsis thaliana lines with altered lignin through down-regulation of hydroxycinnamoyl CoA:shikimate/quinate hydroxycinnamoyl transferase (HCT) or loss of function of cinnamoyl CoA reductase 1 (CCR1) express a suite of pathogenesis-related (PR) protein genes. The plants also exhibit extensive cell wall remodeling associated with induction of multiple cell wall-degrading enzymes, a process which renders the corresponding biomass a substrate for growth of the cellulolytic thermophile Caldicellulosiruptor bescii lacking a functional pectinase gene cluster. The cell wall remodeling also results in the release of size- and charge-heterogeneous pectic oligosaccharide elicitors of PR gene expression. Genetic analysis shows that both in planta PR gene expression and release of elicitors are the result of ectopic expression in xylem of the gene ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE 1 (ADPG1), which is normally expressed during anther and silique dehiscence. These data highlight the importance of pectin in cell wall integrity and the value of lignin modification as a tool to interrogate the informational content of plant cell walls