Genome-wide transcriptome reveals mechanisms underlying Rlm1-mediated blackleg resistance on canola

Abstract

Genetic resistance to blackleg (Leptosphaeria maculans, Lm) of canola (Brassica napus, Bn) has been extensively studied, but the mechanisms underlying the host–pathogen interaction are still not well understood. Here, a comparative transcriptome analysis was performed on a resistant doubled haploid Bn line carrying the resistance gene Rlm1 following inoculation with a virulent (avrLm1) or avirulent (AvrLm1) Lm isolate on cotyledons. A total of 6999 and 3015 differentially expressed genes (DEGs) were identified, respectively, in inoculated local tissues with compatible (susceptible) and incompatible (resistant) interactions. Functional enrichment analysis found several biological processes, including protein targeting to membrane, ribosome and negative regulation of programmed cell death, were over-represented exclusively among up-regulated DEGs in the resistant reaction, whereas significant enrichment of salicylic acid (SA) and jasmonic acid (JA) pathways observed for down-regulated DEGs occurred only in the susceptible reaction. A heat-map analysis showed that both biosynthesis and signaling of SA and JA were induced more significantly in the resistant reaction, implying that a threshold level of SA and JA signaling is required for the activation of Rlm1-mediated resistance. Co-expression network analysis revealed close correlation of a gene module with the resistance, involving DEGs regulating pathogen-associated molecular pattern recognition, JA signaling and transcriptional reprogramming. Substantially fewer DEGs were identified in mock-inoculated (control) cotyledons, relative to those in inoculated local tissues, including those involved in SA pathways potentially contributing to systemic acquired resistance (SAR). Pre-inoculation of cotyledon with either an avirulent or virulent Lm isolate, however, failed to induce SAR on remote tissues of same plant despite elevated SA and PR1 protein. This study provides insights into the molecular mechanism of Rlm1-mediated resistance to blackleg.

Understanding R Gene Evolution in Brassica

“…It has been shown that climate changes, such as variation in the CO 2 concentration, temperature fluctuations and water availability, play a role in influencing disease outcomes in host plants [61]. Disease severity is also impacted by the type of disease resistance of the host, whether it is qualitative or quantitative; in Brassica blackleg disease [62][63][64][65][66][67][68], or in the qualitative type, it depends on the specific pathotype that infects the host. For example, in the B. napus-Pyrenopeziza brassicae (light leaf spot) interaction, the host resistance is specific to the isolated pathotypes [69].…”

Leptosphaeria maculans-Brassica napus Battle: A Comparison of Incompatible vs. Compatible Interactions Using Dual RNASeq

“…Canola ( Brassica napus L.) is the number one cash crop in Canada, contributing CAD 29.9 billion to the national economy annually, including more than 207,000 Canadian jobs and CAD 12 billion in wages [ 1 ]. Annual global and Canadian canola production is estimated as 70 MMT and 18.7 MMT, respectively [ 1 , 2 ]. Blackleg, caused by the actinomycete fungus Leptosphaeria maculans (Desm.)…”

“…Over the past several years, the RNA-seq technique has been widely used to investigate plant pathosystems, including the canola-blackleg system. Several studies have been studied the host system [ 2 , 9 ] and pathogen system [ 48 ] separately. In addition, there were few studies have been studied the whole host-pathosystem by dual RNAseq as well [ 49 ].…”