PacBio full-length transcriptome of wild apple (Malus sieversii) provides insights into canker disease dynamic response

Xiaojie Liu,Bei Gao,Xuejing Wen,Daoyuan Zhang,Xiaoshuang Li,Yu Ding,Yiheng Zhang,Yan Zhang

doi:10.1186/s12864-021-07366-y

Abstract

BackgroundValsa canker is a serious disease in the stem of Malus sieversii, caused by Valsa mali. However, little is known about the global response mechanism in M. sieversii to V. mali infection.ResultsPhytohormone jasmonic acid (JA) and salicylic acid (SA) profiles and transcriptome analysis were used to elaborate on the dynamic response mechanism. We determined that the JA was initially produced to respond to the necrotrophic pathogen V. mali infection at the early response stage, then get synergistically transduced with SA to respond at the late response stage. Furthermore, we adopted Pacific Biosciences (PacBio) full-length sequencing to identify differentially expressed transcripts (DETs) during the canker response stage. We obtained 52,538 full-length transcripts, of which 8139 were DETs. Total 1336 lncRNAs, 23,737 alternative polyadenylation (APA) sites and 3780 putative transcription factors (TFs) were identified. Additionally, functional annotation analysis of DETs indicated that the wild apple response to the infection of V. mali involves plant-pathogen interaction, plant hormone signal transduction, flavonoid biosynthesis, and phenylpropanoid biosynthesis. The co-expression network of the differentially expressed TFs revealed 264 candidate TF transcripts. Among these candidates, the WRKY family was the most abundant. The MsWRKY7 and MsWRKY33 were highly correlated at the early response stage, and MsWRKY6, MsWRKY7, MsWRKY19, MsWRKY33, MsWRKY40, MsWRKY45, MsWRKY51, MsWRKY61, MsWRKY75 were highly correlated at the late stage.ConclusionsThe full-length transcriptomic analysis revealed a series of immune responsive events in M. sieversii in response to V. mali infection. The phytohormone signal pathway regulatory played an important role in the response stage. Additionally, the enriched disease resistance pathways and differentially expressed TFs dynamics collectively contributed to the immune response. This study provides valuable insights into a dynamic response in M. sieversii upon the necrotrophic pathogen V. mali infection, facilitates understanding of response mechanisms to canker disease for apple, and provides supports in the identification of potential resistance genes in M. sieversii.

Highlights

Valsa canker is a serious disease in the stem of Malus sieversii, caused by Valsa mali
salicylic acid (SA) and jasmonic acid (JA) contents changes of M. sieversii responded to the infection of V. mali The necrotic canker symptom in the wounded twig and leaf infected with V. mali was observed at 5 dpi (Fig. 1a)
Previous studies on M. domestica canker disease response transcriptome were mainly based on RNA-Seq method [5], which provided that the chitinreceptors responded to the V. mali infection and SA/JA signaling were involved in the primary phytohormone pathways

Summary

Introduction

Valsa canker is a serious disease in the stem of Malus sieversii, caused by Valsa mali. Wild apple (Malus sieversii) is widely distributed in the Tianshan Wild Fruit Forest area of Xinjiang, China. It is an ancestor of cultivated apple (Malus domestica) distributed in Central Asia to West Europe along the Silk Road [1] and is an isolated ecotype with a homogeneous genetic background that holds the underlying potential for the germplasm improvement of future apple [2]. The area of the Wild Fruit Forest in Xinjiang was dramatically reduced partly due to the M. sieversii was being attacked by the canker disease caused by necrotrophic pathogen Valsa mali and resulting apple tree condition weakening [3, 4]. In wild apple M. sieversii, little is known regarding the integral molecular mechanisms underlying the response to the infection of V. mali

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Discussion

Conclusion