Salicylic acid primed defence response in octoploid strawberry (Benihoppe) leaves induces resistance against Podosphaera aphanis through enhanced accumulation of proanthocyanidins and up-regulation of pathogensis-related genes

Abstract

Background Podosphaera aphanis , a predominately biotrophic fungal pathogen, causes significant yield losses of strawberry. China is the largest strawberry producer in the world, and selecting for powdery mildew-resistant cultivars is desirable. However, the resistance mechanism against P. aphanis in the octoploid strawberry remains unclear. Results To understand the molecular resistance mechanisms, we inoculated strawberry with P. aphanis , and examined the expression profiles of candidate genes and the biochemical phenotypes in strawberry leaves of two groups. The unigenes obtained from salicylic acid (SA)-untreated (SA–) and treated (SA+) leaves resulted in a total of 48,020 and 45,896 genes, respectively. KEGG enrichment showed that phenylpropanoid biosynthesis, plant–pathogen interaction, and plant hormone signal transduction pathways were enriched to a noticeable extent. Comparative analysis demonstrated that genes associated with the SA signalling pathway were significantly upregulated in the strawberry– P. aphanis interaction. In particular, the genes FaTGA , FaDELLA , and FaJAZ negatively regulating salicylic acid SA-responsive genes, whereas FaNPR1 , FaWRKY33 , FaWRKY70 , and FaMYC2 positively regulated SA-responsive genes, leading to increased expression of SA-responsive genes compared to a significant decline in expression of jasmonic acid-responsive genes. Conclusions This study describes the role of total flavonoid content, proanthocyanidins (PAs), pathogenesis-related (PR) proteins, SA, and transcription factors in regulatory model against P. aphanis , which coincided with an early activation of defence, leading to the accumulation of PAs and the production of PR proteins.