Transcriptomics Analysis of Apple Leaves in Response to Alternaria alternata Apple Pathotype Infection

Abstract

Alternaria blotch disease of apple (Malus × domestica Borkh.), caused by the apple pathotype of Alternaria alternata, is one of the most serious fungal diseases to affect apples. To develop an understanding of how apples respond to A. alternata apple pathotype (AAAP) infection, we examined the host transcript accumulation over the period between 0 and 72 h post AAAP inoculation. Large-scale gene expression analysis was conducted of the compatible interaction between “Starking Delicious” apple cultivar and AAAP using RNA-Seq and digital gene expression (DGE) profiling methods. Our results show that a total of 9080 differentially expressed genes (DEGs) were detected (>two-fold and FDR < 0.001) by RNA-Seq. During the early phase of infection, 12 h post inoculation (HPI), AAAP exhibited limited fungal development and little change in the transcript accumulation status (950 DEGs). During the intermediate phase of infection, the period between 18 and 36 HPI, increased fungal development, active infection, and increased transcript accumulation were detected (4111 and 3838 DEGs detected at each time point, respectively). The majority of DEGs were detected by 72 HPI, suggesting that this is an important time point in the response of apples' AAAP infection. Subsequent gene ontology (GO) and pathway enrichment analyses showed that DEGs are predominately involved in biological processes and metabolic pathways; results showed that almost gene associated with photosynthesis, oxidation-reduction were down-regulated, while transcription factors (i.e., WRKY, MYB, NAC, and Hsf) and DEGs involved in cell wall modification, defense signaling, the synthesis of defense-related metabolites, including pathogenesis-related (PRs) genes and phenylpropanoid/cyanoamino acid /flavonoid biosynthesis, were activated during this process. Our study also suggested that the cell wall defensive vulnerability and the down-regulation of most PRs and HSP70s in “Starking Delicious” following AAAP infection might interpret its susceptible to AAAP.

Flavonoid Accumulation Plays an Important Role in the Rust Resistance of Malus Plant Leaves

“…Undoubtedly, the work described in this report is in accordance with the recent reports of Di et al (2017) who suggested that the involvement of SA, ETH and JA signaling in tomato toward susceptibility against pathogen infect and Zhu et al (2017) who suggested flavonoid biosynthesis were activated during apple leaves in response to Alternaria alternata apple pathotype infection this process. Our results provide insights on the flavonoid regulation network, which can be used to improve apple tree breeding and strategies for plant rust resistance.…”

“…Apple leaves infected with Alternaria activated flavonoid biosynthesis and the genes involved in phytohormone signaling pathways (ABA, JA, ETH) were upregulated (Zhu et al, 2017). Sugars and hormones can modulate anthocyanin biosynthesis via the coordinated regulation of the R2R3-MYB/bHLH/WD40(MBW) complex (Das et al, 2012).…”

Time-series expression profiling of sugarcane leaves infected withPuccinia kuehniireveals an ineffective defense system leading to susceptibility

“…447 Other authors observed that upregulation of these genes can be associated with 448 resistance [40,90]. In contrast, phenylpropanoid biosynthesis was enriched at 12 hai in 449 the compatible interaction of an apple cultivar and A. alternata [38]. Furthermore, this 450 pathway was enriched with downregulated genes in cucumber infected by a mutant of 451 hop stunt viroid-grapevine at 28 dai [33].…”

“…Other studies reported chitinases as 422 primary temporal responses in apple and peach plants infected with Alternaria 423 alternata and Xanthomonas arboricola pv. pruni, respectively [38,99], differentially 424 expressed in coconut infected with phytoplasma [100] and in the cacao-Moniliophthora 425 perniciosa pathosystem [37]. Genes involved in the synthesis of this enzyme were 426 induced first at 1 dai and most prominently at 11 days after the inoculation of wheat 427 susceptible to yellow rust [29].…”

“…To achieve an overview of the showed temporary activation at 36 hai of genes encoding these last two enzymes [103]. 445 Several authors noted that genes encoding enzymes of the phenylpropanoid pathway are 446 differentially expressed in the first hours or many days after infection [33,38,39,42]. 447 Other authors observed that upregulation of these genes can be associated with 448 resistance [40,90].…”