Abstract
Although heat shock proteins (HSPs), a family of ubiquitous molecular chaperones, are well characterized in heat stress-related responses, their function in plant defense remains largely unclear. Here, we report the role of VvHSP24, a class B HSP from Vitis vinifera, in β-aminobutyric acid (BABA)-induced priming defense against the necrotrophic fungus Botrytis cinerea in grapes. Grapes treated with 10 mmol L–1 BABA exhibited transiently increased transcript levels of VvNPR1 and several SA-inducible genes, including PR1, PR2, and PR5. Additionally, phytoalexins accumulated upon inoculation with the gray mold fungus B. cinerea, which coincided with the action of a priming mode implicated in pathogen-driven resistance. Intriguingly, electrophoretic mobility shift (EMSA), yeast two-hybrid (Y2H) and His pull-down assays demonstrated that the nuclear chaperone VvHSP24 cannot modulate the transcript of PR genes but does directly interact with VvNPR1 in vivo or in vitro. Furthermore, we found that VvHSP24 overexpression enhanced the transcript levels of NPR1 and SA-responsive genes (PR1, PR2, and PR5) and increased the resistance of transgenic Arabidopsis thaliana to B. cinerea compared with wildtype Col-0. An opposite trend between CRISPR mutants of AtHSFB1 (the orthologous gene of VvHSP24 in Arabidopsis) and wildtype plants was observed. Hence, our results suggest that VvHSP24 has a potential role in NPR1-dependent plant resistance to fungal pathogen. BABA-induced priming defense in grapes may require posttranslational modification of the chaperone VvHSP24 to activate VvNPR1 transcript, leading to PR gene expressions and resistance phenotypes.
Highlights
Grapes are cultivated worldwide with great functional importance in terms of their attractive flavor and constitution of natural phytonutrients (Dai et al, 2011)
According to the phylogenetic tree of Vitis vinifera heat shock transcription factors (HSFs)/heat shock proteins (HSPs) with Arabidopsis thaliana HSFs (AtHSFs), VvHSP24 and AtHSFB1 grouped into class B and a single conserved HSF_DNA-binding domain consisting of 94 amino acids is present at residue ranges of 11–104 and 6–99 in AtHSFB1 and VvHSP24, respectively (Supplementary Figure 3)
GFPtagged VvHSP24 was exclusively detected in the nucleus of onion epidermal cells, contrarily the positive control, i.e., green fluorescent protein (GFP) alone, was found in both the cytoplasm and nucleus (Figure 2)
Summary
Grapes are cultivated worldwide with great functional importance in terms of their attractive flavor and constitution of natural phytonutrients (Dai et al, 2011). The shelf life of postharvest grape berries is very limited, which is mainly ascribed to the invasion of bacterial and fungal pathogens. Gray mold disease by the fungal pathogen Botrytis cinerea has been recognized as one of the most severe epidemics threatening economic effectiveness in fruit crop farming (Feliziani et al, 2013). A variety of B. cinerea strains can secrete mycotoxins and extracellular cell wall-degrading enzymes to disintegrate and digest the host cell walls of vine crops (Gabler et al, 2003). Ongoing application of synthetic fungicides for controlling gray mold rot of grapevines is highly efficiently, but the occurrences of resistance as well as the negative impacts posed by the frequent use of fungicides have gradually threatened the environment. Eco-compatible alternatives for harmful fungicides to suppress the postharvest spoilage of grapes have been urgently demanded (Mari et al, 2014)
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