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ARS Home » Pacific West Area » Wenatchee, Washington » Physiology and Pathology of Tree Fruits Research » Research » Publications at this Location » Publication #297240
Title: Transcriptional regulation of ethylene and jasmonate mediated defense response in apple (Malus domestica) root during Pythium ultimum infection

Author
item Shin, Sung
item LV, JINGYI - Northwest Agriculture And Forestry University
item Mazzola, Mark
item Zhu, Yanmin

Submitted to: Horticulture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2014
Publication Date: 10/29/2014
Citation: Shin, S.B., Lv, J., Mazzola, M., Zhu, Y. 2014. Transcriptional regulation of ethylene and jasmonate mediated defense response in apple (Malus domestica) root during Pythium ultimum infection. Horticulture Research. 1:53.

Interpretive Summary: Apple Replant Disease (ARD) causes a serious economic loss for the apple industry. Use of resistant rootstock is a sustainable approach with economical and environmental advantages. It is known that a complex of necrotrophic fungi and oomycetes incite ARD, but the genes which are responsible for the resistance or tolerance in apple root system to these pathogens has not been examined. In this study, we identified the apple genes that are activated by Pythium ultimum, a pathogenic oomycetes that is a significant component of the ARD pathogen complex. The apple genes functioned in plant hormone ethylene (ET) and jasmonic acid (JA) biosynthesis, and a gene for transcription factor, MdERF1, that functions as an ET/JA signal integrator were activated in response to P. ultimum inoculation. With a sensitive detection method of quantitative reverse transcription PCR, the target genes expression exhibited a 10-60 fold up-regulation in apple root stock seedlings 1-2 days post P. ultimum inoculation, compared to mock inoculation. Exogenous application of ET and/or JA hormones also increased the expression level of these genes. MdERF1 was not only up-regulated by either ethylene or JA, but with significantly greater up-regulation when exposed to the combination of these hormones. Our work demonstrated for the first time that ET/JA mediated signal network functions in the root system of perennial tree crops in respond to infection by P. ultimum.

Technical Abstract: Apple Replant Disease (ARD) causes a serious economic loss for the apple industry. Although it has been known that a complex of necrotrophic fungi and oomycetes are the primary causal agent of ARD, the genetic response in apple to infection by these pathogens has not previously been examined. In this study, we identified the apple genes that are activated by Pythium ultimum, a pathogenic oomycetes that is a significant component of the ARD pathogen complex. The apple genes examined in this study included ethylene (ET) biosynthesis gene (MdACS: 1-aminocyclopropane-1-carboxylic acid synthase), jasmonic acid (JA) biosynthesis gene (MdAOS: allene oxide synthase), and a transcription factor gene that functions as an ET/JA signal integrator (MdERF1: ethylene response factor1). With real-time quantitative reverse transcription PCR, the target genes expression exhibited a 10-60 fold up-regulation in apple root stock seedlings 1-2 days post P. ultimum inoculation. Transcriptional regulation of these target genes by ET/JA hormonal signals was also examined. MdERF1 was not only up-regulated by either ethylene or JA, but the enhanced expression of MdERF1 was significantly greater when exposed to the combination of these hormones. For MdACS and MdAOS, ethylene and JA serve as a positive or negative regulator depending upon gene isoform and the plant tissues in which expression is monitored. Therefore, we conclude that there may exist a complicated ET/JA network for the transcriptional regulation of apple genes that respond to infection by P. ultimum.