Suppression of abscisic acid biosynthesis at the early infection stage of Verticillium longisporum in oilseed rape (Brassica napus).

Falk H Behrens,Lena Ladewig,Thomas Bergmann,Yan Zhao,Wanzhi Ye,Markus Schemmel,Claudia Häder,Wenxuan Zhu,Roxana Hossain,Daguang Cai,Dirk Schenke

doi:10.1111/mpp.12867

Abstract

Summary Verticillium longisporum infects oilseed rape (Brassica napus) and Arabidopsis thaliana. To investigate the early response of oilseed rape to the fungal infection, we determined transcriptomic changes in oilseed rape roots at 6 days post‐inoculation (dpi) by RNA‐Seq analysis, in which non‐infected roots served as a control. Strikingly, a subset of genes involved in abscisic acid (ABA) biosynthesis was found to be down‐regulated and the ABA level was accordingly attenuated in 6 dpi oilseed rape as compared with the control. Gene expression analysis revealed that this was mainly attributed to the suppression of BnNCED3‐mediated ABA biosynthesis, involving, for example, BnWRKY57. However, this down‐regulation of ABA biosynthesis could not be observed in infected Arabidopsis roots. Arabidopsis ABA‐ defective mutants nced3 and aao3 displayed pronounced tolerance to the fungal infection with delayed and impeded symptom development, even though fungal colonization was not affected in both mutants. These data suggest that ABA appears to be required for full susceptibility of Arabidopsis to the fungal infection. Furthermore, we found that in both 6 dpi oilseed rape and the Arabidopsis nced3 mutant, the salicylic acid (SA) signalling pathway was induced while the jasmonic acid (JA)/ethylene (ET) signalling pathway was concomitantly mitigated. Following these data, we conclude that in oilseed rape the V. longisporum infection triggers a host‐specific suppression of the NCED3‐mediated ABA biosynthesis, consequently increasing plant tolerance to the fungal infection. We believe that this might be part of the virulence strategy of V. longisporum to initiate/establish a long‐lasting compatible interaction with oilseed rape (coexistence), which appears to be different from the infection process in Arabidopsis.

Highlights

Brassica napus is an important oilseed crop grown worldwide and the cultivated area of oilseed rape has continuously increased in recent years (FAOSTAT, 2016)
To investigate the early response of oilseed rape plants to the fungal infection, transcriptomic changes in oilseed rape roots in response to infection with V. longisporum isolate 43 (Vl43) were investigated by RNA-Seq at 6 dpi, in which non-infected roots served as a control
gene ontology (GO) terms for responses to abscisic acid (ABA) and ABA biosynthesis were one of the most affected biological processes in B. napus (Table 1); we investigated the general biosynthesis of the phytohormones salicylic acid (SA), jasmonic acid (JA), ET and ABA upon the GO terms in more detail (Fig. 1), revealing a significant difference between the plant species with respect to ABA biosynthesis

Summary

SUMMARY

Verticillium longisporum infects oilseed rape (Brassica napus) and Arabidopsis thaliana. Gene expression analysis revealed that this was mainly attributed to the suppression of BnNCED3-mediated ABA biosynthesis, involving, for example, BnWRKY57 This down-regulation of ABA biosynthesis could not be observed in infected Arabidopsis roots. We found that in both 6 dpi oilseed rape and the Arabidopsis nced mutant, the salicylic acid (SA) signalling pathway was induced while the jasmonic acid (JA)/ethylene (ET) signalling pathway was concomitantly mitigated. Following these data, we conclude that in oilseed rape the V. longisporum infection triggers a hostspecific suppression of the NCED3-mediated ABA biosynthesis, increasing plant tolerance to the fungal infection.

INTRODUCTION

Findings

DISCUSSION

EXPERIMENTAL PROCEDURES