Abstract
While our understanding of the genetics underlying the Brassica-Leptosphaeria pathosystem has advanced greatly in the last decade, differences in molecular responses due to interaction between resistance genes and host genetic background has not been studied. We applied RNAseq technology to monitor the transcriptome profiles of Brassica napus (Bn) lines carrying one of four blackleg R genes (Rlm2, Rlm3, LepR1 & LepR2) in Topas or Westar background, during the early stages of infection by a Leptosphaeria maculans (Lm) isolate carrying the corresponding Avr genes. We observed upregulation of host genes involved in hormone signalling, cell wall thickening, response to chitin and glucosinolate production in all R gene lines at 3 day after inoculation (dai) albeit having higher level of expression in LepR1 and Rlm2 than in Rlm3 and LepR2 lines. Bn-SOBIR1 (Suppressor Of BIR1-1), a receptor like kinase (RLK) that forms complex receptor like proteins (RLPs) was highly expressed in LepR1 and Rlm2 at 3 dai. In contrast Bn-SOBIR1 induction was low in Rlm3 line, which could indicate that Rlm3 may function independent of SOBIR1. Expression of Salicylic acid (SA) related defense was enhanced in LepR1 and Rlm2 at 3 dai. In contrast to SA, expression of Bn genes with homology to PDF1.2, a jasmonic acid (JA) pathway marker, were increased in all Rlm and LepR lines at 6 and 9 dai. Effect of host genetic background on induction of defense, was determined by comparison of LepR1 and LepR2 in Topas vs Westar genotype (i.e. T-LepR1 vs W-LepR1 and T-LepR2 vs W-LepR2). In both cases (regardless of R gene) overall number of defense related genes at the earliest time point (3 dai) was higher in Tops compared to Westar. SA and JA markers genes such as PR1 and PDF1.2 were more induced in Topas compared to Westar introgression lines at this time point. Even in the absence of any R gene, effect of Topas genotype in enhanced defense, was also evident by the induction of PDF1.2 that started at a low level at 3 dai and peaked at 6 and 9 dai, while no induction in Westar genotype was observed at any of these time points. Overall, variation in time and intensity of expression of genes related to defense, was clearly dependent on both R gene and the host genotype.
Highlights
Www.nature.com/scientificreports is up-regulated at the later stages (6–9 dai)
We have introduced individual Rlm and LepR (Leptosphaeria resistance) genes into the common susceptible Brassica napus (Bn) cultivar Topas using repeated backcrossing and selfing (BC5S3) that allowed generation of individual Topas lines each harbouring Rlm or LepR gene intervals which was confirmed by genome wide high density SNP profiling of each line, minimizing background effects on R gene performance[13]
We have previously noted that the cotyledon immune response triggered by R genes in Topas is often more robust compared to the immune response induced by the same R gene in Westar[13]
Summary
Www.nature.com/scientificreports is up-regulated at the later stages (6–9 dai). Induction of JA defense correlates with the up-regulation of the Lm gene necrosis and ethylene‐inducing peptide‐1 (Nep‐1) ‐like protein, a well-known marker of transition from biotrophy to necrotrophy in fungi[4]. Despite being a qualitative trait, the immunity response triggered by R gene Avr gene recognition varies in phenotype; from a highly-localised response seen as minute necrosis, trailing necrosis, no visual symptoms or contained pathogen growth and sporulation[6] Both genotype of the host and functional variation of R genes cause variation in the interaction phenotype[7]. This led to generation of seven Topas introgression lines (T-Rlm[1], T-Rlm[2], T-Rlm[3], T-Rlm[4], T-LepR1, T-LepR2, T-LepR3), which share 92.9–98.9% of their genomic background with the susceptible parental lines[13], and two Westar introgression lines (1065; W-LepR1, 1135; W-LepR2) These introgression lines provide a unique tool to compare the function of different R genes in a common genotype background and for the dissection of the effect of host genetic background on the defense responses triggered by the same R gene. We describe the differences in gene expression profiles and defense pathways among these treatments and their correlation with the variation in visual interaction phenotypes
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
