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Characterization of winter squash age-related resistance to Phytophthora capsici through fruit peel transcriptome profiling

Safa Alzohairy: Department of Plant Soil and Microbial Sciences, Michigan State University

<div>Fruit of winter squash (<em>Cucurbita moschata</em>) cultivars develop resistance to the oomycete plant pathogen <em>Phytophthora capsici</em> 21 days post pollination (dpp); young fruit (7 dpp) are susceptible. This phenomenon is known as age-related resistance (ARR). Previous studies demonstrated that exocarp cuticle and epidermal walls are thicker at 21 dpp than at 7 dpp and that wounding of mature fruit results in susceptibility. To determine the molecular mechanisms of ARR, two <em>C. moschata</em> cultivars (‘Chieftain’ and ‘Dickenson’) that exhibit different ARR onsets were selected for transcriptome profiling with RNA-sequencing. The sequencing was conducted using RNA samples from fruit at the following dpp: 7, 10, 14, and 21 from ‘Chieftain’ that develops ARR at 14 dpp and ‘Dickenson’ that develops ARR at 21 dpp. Functional annotation of the differentially up-regulated genes in the resistant fruit peel relative to the susceptible one revealed enrichment for genes associated with cell wall structures biosynthesis. Pathway enrichment analysis revealed enrichment of the upregulated genes in cutin, suberin monomers and phenylpropanoids biosynthesis. Our findings suggested that ARR is highly associated with monolignols biosynthesis and lignin deposition at the cell wall of the resistant fruit peel. This is the first time that transcriptome profiling has been used to uncover the mechanisms of ARR in winter squash to <em>P. capsici</em>. Identifying the genetic mechanism of ARR in winter squash will facilitate the development of <em>Cucurbita</em> varieties with resistance to <em>P. capsici</em> and assist the development of <em>P. capsici</em> disease management schemes for producers’ benefit.</div>