Abstract
Fatty acid hydroperoxides can generate short-chained volatile aldehydes that may participate in plant defence. A grapevine hydroperoxide lyase (VvHPL1) clustering to the CYP74B class was functionally characterized with respect to a role in defence. In grapevine leaves, transcripts of this gene accumulated rapidly to high abundance in response to wounding. Cellular functions of VvHPL1 were investigated upon heterologous expression in tobacco BY-2 cells. A C-terminal green fluorescent protein (GFP) fusion of VvHPL1 was located in plastids. The overexpression lines were found to respond to salinity stress or the bacterial elicitor harpin by increasing cell death. This signal-dependent mortality response was mitigated either by addition of exogenous jasmonic acid or by treatment with diphenyleneiodonium (DPI), an inhibitor of NADPH oxidases. By feeding different substrates to recombinantly expressed enzyme, VvHPL1 could also be functionally classified as true 13-HPL. The cognate products generated by this 13-HPL were cis-3-hexenal and trans-2-hexenal. Using a GFP-tagged actin marker line, one of these isomeric products, cis-3-hexenal, was found specifically to elicit a rapid disintegration of actin filaments. This response was not only observed in the heterologous system (tobacco BY-2), but also in a grapevine cell strain expressing this marker, as well as in leaf discs from an actin marker grape used as a homologous system. These results are discussed in the context of a role for VvHPL1 in a lipoxygenase-dependent signalling pathway triggering cell death-related defence that bifurcates from jasmonate-dependent basal immunity.
Highlights
Plant immunity relies, to a large degree, on inducible defence
The plant response to pathogens is complex and composed of at least two layers: a basal, broad-band immunity [pathogen-associated molecular pattern (PAMP)-triggered immunity, PTI] co-exists with a strain-specific level of immunity, which often culminates in a specific type of programmed cell death (PCD) termed hypersensitive response (HR) and originates from a Abbreviations.AOS, allene oxide synthase; BY-2, tobacco Nicotiana tabacum L. cv. bright yellow 2; CYP, cytochrome P450; DPI, diphenyleneiodonium; ETI, effectortriggered immunity; GFP, green fluorescent protein; green leaf volatiles (GLVs), green leaf volatile; HPL, hydroperoxide lyase; HPOD, hydroperoxy octadecadienoic acid; HPOT, hydroperoxy octadecatrienoic acid; HR, hypersensitive response; JA, jasmonic acid; JA-Ile, (+)-7-iso-jasmonoyl-l-isoleucine; PAMP, pathogen-associated molecular pattern; PCD, programmed cell death; PTI, PAMP-triggered immunity; ROS, reactive oxygen species; SBSE, stir bar sorptive extraction; WT, wild type
The VvMTh-HPL1 protein is identical to a protein which has been isolated from the V. vinifera cultivar ‘Cabernet Sauvignon’, except for one residue, and shown experimentally to be a canonical CYP74B accepting 13-HPOD/T as substrates (Zhu et al, 2012)
Summary
To a large degree, on inducible defence. The plant response to pathogens is complex and composed of at least two layers: a basal, broad-band immunity [pathogen-associated molecular pattern (PAMP)-triggered immunity, PTI] co-exists with a strain-specific level of immunity (effector-triggered immunity, ETI), which often culminates in a specific type of programmed cell death (PCD) termed hypersensitive response (HR) and originates from a Abbreviations.AOS, allene oxide synthase; BY-2, tobacco Nicotiana tabacum L. cv. bright yellow 2; CYP, cytochrome P450; DPI, diphenyleneiodonium; ETI, effectortriggered immunity; GFP, green fluorescent protein; GLV, green leaf volatile; HPL, hydroperoxide lyase; HPOD, hydroperoxy octadecadienoic acid; HPOT, hydroperoxy octadecatrienoic acid; HR, hypersensitive response; JA, jasmonic acid; JA-Ile, (+)-7-iso-jasmonoyl-l-isoleucine; PAMP, pathogen-associated molecular pattern; PCD, programmed cell death; PTI, PAMP-triggered immunity; ROS, reactive oxygen species; SBSE, stir bar sorptive extraction; WT, wild type.2884 | Akaberi et al.co-evolutionary history between host and pathogen (Jones and Dangl, 2006).The qualitatively different output of PTI and ETI would suggest that the underlying signalling must be different. Bright yellow 2; CYP, cytochrome P450; DPI, diphenyleneiodonium; ETI, effectortriggered immunity; GFP, green fluorescent protein; GLV, green leaf volatile; HPL, hydroperoxide lyase; HPOD, hydroperoxy octadecadienoic acid; HPOT, hydroperoxy octadecatrienoic acid; HR, hypersensitive response; JA, jasmonic acid; JA-Ile, (+)-7-iso-jasmonoyl-l-isoleucine; PAMP, pathogen-associated molecular pattern; PCD, programmed cell death; PTI, PAMP-triggered immunity; ROS, reactive oxygen species; SBSE, stir bar sorptive extraction; WT, wild type. A comparative study in grapevine cells (Chang and Nick, 2012) has revealed that the early signals for PTI and ETI are mostly identical, but are generated in a different temporal pattern. One of these generic signals are reactive oxygen species (ROS). RboH was shown to regulate defence-related cell death through modulating actin organization (Chang et al, 2015), or to activate innate immunity by activation of the transcription factor gene MYB14 that up-regulates stilbene synthase, a key enzyme of phytoalexin synthesis (Duan et al, 2016)
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