Expression profiling of marker genes responsive to the defence-associated phytohormones salicylic acid, jasmonic acid and ethylene in Brachypodium distachyon

Abstract

BackgroundBrachypodium distachyon is a promising model plants for grasses. Infections of Brachypodium by various pathogens that severely impair crop production have been reported, and the species accordingly provides an alternative platform for investigating molecular mechanisms of pathogen virulence and plant disease resistance. To date, we have a broad picture of plant immunity only in Arabidopsis and rice; therefore, Brachypodium may constitute a counterpart that displays the commonality and uniqueness of defence systems among plant species. Phytohormones play key roles in plant biotic stress responses, and hormone-responsive genes are used to qualitatively and quantitatively evaluate disease resistance responses during pathogen infection. For these purposes, defence-related phytohormone marker genes expressed at time points suitable for defence-response monitoring are needed. Information about their expression profiles over time as well as their response specificity is also helpful. However, useful marker genes are still rare in Brachypodium.ResultsWe selected 34 candidates for Brachypodium marker genes on the basis of protein-sequence similarity to known marker genes used in Arabidopsis and rice. Brachypodium plants were treated with the defence-related phytohormones salicylic acid, jasmonic acid and ethylene, and their transcription levels were measured 24 and 48 h after treatment. Two genes for salicylic acid, 7 for jasmonic acid and 2 for ethylene were significantly induced at either or both time points. We then focused on 11 genes encoding pathogenesis-related (PR) 1 protein and compared their expression patterns with those of Arabidopsis and rice. Phylogenetic analysis suggested that Brachypodium contains several PR1-family genes similar to rice genes. Our expression profiling revealed that regulation patterns of some PR1 genes as well as of markers identified for defence-related phytohormones are closely related to those in rice.ConclusionWe propose that the Brachypodium immune hormone marker genes identified in this study will be useful to plant pathologists who use Brachypodium as a model pathosystem, because the timing of their transcriptional activation matches that of the disease resistance response. Our results using Brachypodium also suggest that monocots share a characteristic immune system, defined as the common defence system, that is different from that of dicots.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0749-9) contains supplementary material, which is available to authorized users.

Detection of race-specific resistance against Puccinia coronata f. sp. avenae in Brachypodium species

“…avenae . The Pathogenesis-related ( PR ) genes PR1 and PR5 were upregulated in response to all rust isolates and given that PR1 is a key marker gene of SA signaling (Kouzai et al 2016; Sels et al 2008), this further supports that the activation of SA-dependent defense responses may contribute to the phenotypes observed in B. distachyon and B. hybridum during P. coronata f. sp. avenae infection.…”

Salicylic acid‐dependent immunity contributes to resistance against Rhizoctonia solani, a necrotrophic fungal agent of sheath blight, in rice and Brachypodium distachyon

“…During the infection of R. solani , the SA marker genes BdWRKY45L1 and BdWRKY45L2 were transcribed within 5 and 24 hpi in Bd3‐1 and Gaz‐4, respectively, but not in Bd21 (Fig. c) (Kouzai et al ., ), suggesting the activation of ETI in these R. solani ‐resistant accessions. By contrast, the JA marker BdAOS was clearly induced only in Bd21 (Kouzai et al ., ).…”

“…These compounds induced the transcription of BdWRKY45L1 ( Bradi2 g30695 ), a marker gene for SA response, after 24 h of treatment in B. distachyon (Fig. c) (Kouzai et al ., ). The B. distachyon leaves were then treated with these analogs for 24 h, followed by inoculation with R. solani .…”

Linking Dynamic Phenotyping with Metabolite Analysis to Study Natural Variation in Drought Responses of Brachypodium distachyon

“…Expression profiling of markers for defense-related phytohormones showed that Brachypodium has phytohormone responses more similar to those of rice than of Arabidopsis, suggesting that monocots share a common defense system that is different from that of dicots (Kouzai et al, 2016). Our analyses identified relative higher levels of GA, SA, and JA in the TOL ecotypes when exposed to severe drought with the latter also higher in TOL lines under mild drought.…”