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In this study, we investigated the interplay between nitrogen nutrition and the pectin degradation dynamics during Arabidopsis and Botrytis interaction. Our findings revealed that infected detached leaves from nitrogen-sufficient plants released more pectin lyase (PNL)-derived oligogalacturonides compared to nitrogen-deficient ones. We then focused on BcPNL1, the most highly expressed Botrytis PNL upon infection. Using mutant strains lacking BcPNL1, we observed reduced pathogenicity, a delay in germination and a lag in triggering the plant defense response. Additionally, in nitrogen-sufficient detached leaves, the elevated expression of jasmonic acid repressor genes observed upon infection with the wild-type strain was abolished with the mutants. These results linked the increased production of BcPNL-derived products to the increased expression of jasmonic acid repressor genes, contributing partially to the higher susceptibility of nitrogen-sufficient detached leaves. These findings could lay the foundation for new strategies aimed at reconciling both crop resistance to pathogens and the improvement of nitrogen nutrition. The Botrytis cinerea pectin lyase BcPNL1 produces oligogalacturonides that activate expression of jasmonic acid repressor genes, contributing partially to the higher susceptibility of nitrogen-sufficient detached leaves. [ABSTRACT FROM AUTHOR]

Although angiosperm plants generally react to immunity elicitors like chitin or chitosan by the cell wall callose deposition, this response in particular cell types, especially upon chitosan treatment, is not fully understood. Here we show that the growing root hairs (RHs) of Arabidopsis can respond to a mild (0.001%) chitosan treatment by the callose deposition and by a deceleration of the RH growth. We demonstrate that the glucan synthase‐like 5/PMR4 is vital for chitosan‐induced callose deposition but not for RH growth inhibition. Upon the higher chitosan concentration (0.01%) treatment, RHs do not deposit callose, while growth inhibition is prominent. To understand the molecular and cellular mechanisms underpinning the responses to two chitosan treatments, we analysed early Ca2+ and defence‐related signalling, gene expression, cell wall and RH cellular endomembrane modifications. Chitosan‐induced callose deposition is also present in the several other plant species, including functionally analogous and evolutionarily only distantly related RH‐like structures such as rhizoids of bryophytes. Our results point to the RH callose deposition as a conserved strategy of soil‐anchoring plant cells to cope with mild biotic stress. However, high chitosan concentration prominently disturbs RH intracellular dynamics, tip‐localised endomembrane compartments, growth and viability, precluding callose deposition. Summary statement: The root hairs (RHs) of Arabidopsis, when exposed to elicitor chitosan, deposit callose and change the growth rate. This is accompanied by altered signalling, gene expression, and is linked to altered pectin methylation state. Our research highlights the evolutionarily conserved role of RHs in environmental sensing. [ABSTRACT FROM AUTHOR]