AUTHOR=Nunes da Silva M. , Vasconcelos M. W. , Gaspar M. , Balestra G. M. , Mazzaglia A. , Carvalho Susana M. P. 

TITLE=Early Pathogen Recognition and Antioxidant System Activation Contributes to Actinidia arguta Tolerance Against Pseudomonas syringae Pathovars actinidiae and actinidifoliorum

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.01022

DOI=10.3389/fpls.2020.01022

ISSN=1664-462X

ABSTRACT=<p><italic>Actinidia chinensis</italic> and <italic>A. arguta</italic> have distinct tolerances to <italic>Pseudomonas syringae</italic> pv. <italic>actinidiae</italic> (Psa), but the reasons underlying the inter-specific variation remain unclear. This study aimed to integrate the metabolic and molecular responses of these two kiwifruit species against the highly pathogenic Psa and the less pathogenic <italic>P. syringae</italic> pv. <italic>actinidifoliorum</italic> (Pfm) bacterial strains. Disease development was monitored weekly till 21 days post inoculation (dpi), analysing a broad number and variety of parameters including: colony forming units (CFU), foliar symptoms, total chlorophylls, lipid peroxidation, soluble polyphenols, lignin and defense-related gene expression. At the end of the experimental period <italic>A. chinensis</italic> inoculated with Psa presented the highest endophytic bacterial population, whereas <italic>A. arguta</italic> inoculated with Pfm showed the lowest values, also resulting in a lower extent of leaf symptoms. Metabolic responses to infection were also more pronounced in <italic>A. chinensis</italic> with decreased total chlorophylls (up to 55%) and increased lipid peroxidation (up to 53%), compared with non-inoculated plants. Moreover, at 14 dpi soluble polyphenols and lignin concentrations were significantly higher (112 and 26%, respectively) in Psa-inoculated plants than in controls, while in <italic>A. arguta</italic> no significant changes were observed in those metabolic responses, except for lignin concentration which was, in general, significantly higher in Psa-inoculated plants (by at least 22%), comparing with control and Pfm-inoculated plants. Genes encoding antioxidant enzymes (<italic>SOD</italic>, <italic>APX</italic> and <italic>CAT</italic>) were upregulated at an earlier stage in Psa-inoculated <italic>A. arguta</italic> than in <italic>A. chinensis</italic>. In contrast, genes related with phenylpropanoids (<italic>LOX1</italic>) and ethylene (<italic>SAM</italic>) pathways were downregulated in <italic>A. arguta</italic>, but upregulated in <italic>A. chinensis</italic> in the later phases of infection. Expression of <italic>Pto3</italic>, responsible for pathogen recognition, occurred 2 dpi in <italic>A. arguta</italic>, but only 14 dpi in <italic>A. chinensis</italic>. In conclusion, we found that <italic>A. arguta</italic> is more tolerant to Psa and Pfm infection than <italic>A. chinensis</italic> and its primary and secondary metabolism is less impacted. <italic>A. arguta</italic> higher tolerance seems to be related with early pathogen recognition, the activation of plant antioxidant system, and to the suppression of ET and JA pathways from an earlier moment after infection.</p>