Abstract
Apple scab disease caused by the fungus Venturia inaequalis is a devastating disease that seriously affects quality and yield of apples. In order to understand the mechanisms involved in scab resistance, we performed gas chromatography-mass spectrometry based metabolomics analysis of the cell culture of scab resistant cultivar ‘Florina’ and scab susceptible cultivar ‘Vista Bella’ both prior -to and -following treatment with V. inaequalis elicitor (VIE). A total 21 metabolites were identified to be altered significantly in ‘Florina’ cell cultures upon VIE-treatment. Among 21 metabolites, formation of three new specialized metabolites aucuparin, noraucuparin and eriobofuran were observed only in resistant cultivar ‘Florina’ after the elicitor treatment. The score plots of principal component analysis (PCA) exhibited clear discrimination between untreated and VIE-treated samples. The alteration in metabolite levels correlated well with the changes in the transcript levels of selected secondary metabolite biosynthesis genes. Aucuparin, noraucuparin and eriobofuran isolated from the ‘Florina’ cultures showed significant inhibitory effect on the conidial germination of V. inaequalis. The results expand our understanding of the metabolic basis of scab-resistance in apple and therefore are of interest in apple breeding programs to fortify scab resistance potential of commercially grown apple cultivars.
Highlights
Apple (Malus domestica) is the main deciduous fruit crop of the temperate region of the world[1]
In order to understand metabolic re-programming following V. inaequalis elicitor (VIE)-treatment, metabolomics was performed on samples prepared from treated scab resistant (SR) and SS cell cultures at 6, 12, 24, 36, 48 and 72 hours post elicitation and control (SR0 and SS0) untreated cultures
Metabolites were profiled by gas chromatography-mass spectrometry (GC-MS) metabolomics analyses, comparing the levels of each metabolite at defined time points to the equivalent un-treated controls
Summary
Apple (Malus domestica) is the main deciduous fruit crop of the temperate region of the world[1]. Strategies able to directly transfer traits to elite cultivated varieties through cis-genic approach would accelerate the breeding process[19] Several apple cultivars such as ‘Liberty’, ‘Florina’, ‘Prima’, ‘Sir Prize’ are resistant to scab infections. The HR in apples are exhibited by several previously characterized ‘R’ genes such as Rvi[4], Rvi[5], Rvi[7], Rvi[10], Rvi[15] and Rvi1618 that produces typical “pin-point pits” These pin-point-pits are formed as a result of rapid death and subsequent collapse of cells immediately surrounding the germinating spore penetration site[23]. It was reported that pathogenicity related proteins like β-1,3-glucanase, chitinase, and thaumatin-like protein were constitutively expressed in the apoplast of the resistant apple cultivar ‘Remo’ and were induced in susceptible cultivar ‘Elstar’ after V. inaequalis infection[33]. Cis-genic apple lines of the cultivars ‘Brookfield Baigent’, ‘Mitchgla’, ‘Novajo’, and ‘Pinova’ harboring Rvi[6] gene showed enhanced scab resistance[19]
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