Abstract
Botryosphaeria dothidea is a pathogen with worldwide distribution, infecting hundreds of species of economically important woody plants. It infects and causes various symptoms on apple plants, including wart and canker on branches, twigs, and stems. However, the mechanism of warts formation is unclear. In this study, we investigated the mechanism of wart formation by observing the transection ultrastructure of the inoculated cortical tissues at various time points of the infection process and detecting the expression of genes related to the pathogen pathogenicity and plant defense response. Results revealed that wart induced by B. dothidea consisted of proliferous of phelloderm cells, the newly formed secondary phellem, and the suberized phelloderm cells surrounding the invading mycelia. The qRT-PCR analysis revealed the significant upregulation of apple pathogenesis-related and suberification-related genes and a pathogen cutinase gene Bdo_10846. The Bdo_10846 knockout transformants showed reduced cutinase activity and decreased virulence. Transient expression of Bdo_10846 in Nicotiana benthamiana induced ROS burst, callose formation, the resistance of N. benthamiana to Botrytis cinerea, and significant upregulation of the plant pathogenesis-related and suberification-related genes. Additionally, the enzyme activity is essential for the induction. Virus-induced gene silencing demonstrated that the NbBAK1 and NbSOBIR1 expression were required for the Bdo_10846 induced defense response in N. benthamiana. These results revealed the mechanism of wart formation induced by B. dothidea invasion and the important roles of the cutinase Bdo_10846 in pathogen virulence and in inducing plant immunity.
Highlights
Botryosphaeria dothidea is a pathogen with worldwide distribution, infecting hundreds of species of economically important woody plants, including apple, pear, grape, blueberry, poplar, and eucalyptus [1]
We investigate the mechanism of warts formation on apple shoots and explore the role of a cutinase gene in the interaction between B. dothidea and the apple (Malus domestica) plant
To investigate the wart formation, we inoculated the unwounded apple shoots with mycelial blocks of B. dothidea, and warts formed on the inoculated shoots around 30 dpi (Figure 1 and Figure S1B)
Summary
Botryosphaeria dothidea is a pathogen with worldwide distribution, infecting hundreds of species of economically important woody plants, including apple, pear, grape, blueberry, poplar, and eucalyptus [1]. It causes fruit rot, wart, and canker on twigs, branches, and stems, dieback of twigs and branches, or plant death, and is a constant threat to agriculture, commercial forest industry, and native ecosystems [1,2,3,4,5]. The phellem layer in the cortex of root and stem, which consists of suberin, serves as a physical barrier at the interface between the secondary development tissue and the environment [9]
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