Abstract
BackgroundForage and turf grasses are routinely cut and grazed upon throughout their lifecycle. When grasses are cut or damaged, they rapidly release a volatile chemical cocktail called green leaf volatiles (GLV). Previously we have shown that mechanical wounding or exposure to GLV released from cut grass, activated a Lt 46 kDa mitogen-activated protein kinase (MAPK) within 3 min and a 44 kDa MAPK within 15–20 min in the model grass species Lolium temulentum (Lt). Currently very little is known concerning the perception, signaling or molecular responses associated with wound stress in grasses. Since GLV are released during wounding, we wanted to investigate what genes and signaling pathways would be induced in undamaged plants exposed to GLV.ResultsRNA-Seq generated transcriptome of Lolium plants exposed to GLV identified 4308 up- and 2794 down-regulated distinct differentially-expressed sequences (DES). Gene Ontology analysis revealed a strong emphasis on signaling, response to stimulus and stress related categories. Transcription factors and kinases comprise over 13% of the total DES found in the up-regulated dataset. The analysis showed a strong initial burst within the first hour of GLV exposure with over 60% of the up-regulated DES being induced. Specifically sequences annotated for enzymes involved in the biosynthesis of jasmonic acid and other plant hormones, mitogen-activated protein kinases and WRKY transcription factors were identified. Interestingly, eleven DES for ferric reductase oxidase, an enzyme involved in iron uptake and transport, were exclusively found in the down-regulated dataset. Twelve DES of interest were selected for qRT-PCR analysis; all displayed a rapid induction one hour after GLV exposure and were also strongly induced by mechanical wounding.ConclusionThe information gained from the analysis of this transcriptome and previous studies suggests that GLV released from cut grasses transiently primes an undamaged plant’s wound stress pathways for potential oncoming damage, and may have a dual role for inter- as well as intra-plant signaling.
Highlights
Damage to plant tissues due to feeding insects, the grazing of animals, plants crushed by being tread upon or by being mechanically cut is a major form of stress that all plants must endure
We have shown that mechanical wounding and green leaf volatiles (GLV) released from cut grass activated a 46 kDa mitogenactivated protein kinase (MAPK) within 3 min and 44 kDa MAPK within 20 min after wounding or exposure to GLVs in Lolium temulentum (Lt) [72, 76, 77]
The initial read counts and percent alignments for expression libraries generated for Lt plants after exposure to the GLV are summarized in Additional file 2: Table S2
Summary
Damage to plant tissues due to feeding insects, the grazing of animals, plants crushed by being tread upon or by being mechanically cut is a major form of stress that all plants must endure. Jasmonate biosynthesis originates in the chloroplast through the release and conversion of polyunsaturated fatty acids The release of these fatty acids is through the action of lipases, linolenic acid by phospholipase A (PLA) [21, 22]. These long-chain fatty acids are oxidized through lipoxygenase-catalyzed reactions and are converted to 13-hydroperoxy derivatives. We have shown that mechanical wounding or exposure to GLV released from cut grass, activated a Lt 46 kDa mitogenactivated protein kinase (MAPK) within 3 min and a 44 kDa MAPK within 15–20 min in the model grass species Lolium temulentum (Lt). Since GLV are released during wounding, we wanted to investigate what genes and signaling pathways would be induced in undamaged plants exposed to GLV
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