Abstract
Apple russeting develops on the fruit surface when skin integrity has been lost. It induces a modification of fruit wax composition, including its triterpene profile. In the present work, we studied two closely related apple varieties, ‘Reinette grise du Canada’ and ‘Reinette blanche du Canada’, which display russeted and non-russeted skin phenotypes, respectively, during fruit development. To better understand the molecular events associated with russeting and the differential triterpene composition, metabolomics data were generated using liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) and combined with proteomic and transcriptomic data. Our results indicated lower expression of genes linked to cuticle biosynthesis (cutin and wax) in russet apple throughout fruit development, along with an alteration of the specialized metabolism pathways, including triterpene and phenylpropanoid. We identified a lipid transfer protein (LTP3) as a novel player in cuticle formation, possibly involved in the transport of both cutin and wax components in apple skin. Metabolomic data highlighted for the first time a large diversity of triterpene-hydroxycinnamates in russeted tissues, accumulation of which was highly correlated with suberin-related genes, including some enzymes belonging to the BAHD (HXXXD-motif) acyltransferase family. Overall, this study increases our understanding about the crosstalk between triterpene and suberin pathways.
Highlights
Apple production is a major horticultural sector with 87 million tons produced in 2019 (FAOSTAT, https://www.fao.org/home)
While previous studies focused on the analysis of RNA-sequencing data, we studied the two contrasting varieties using a combination of metabolomics, proteomics, and transcriptomics data
CG exhibited russeting at 57 days after full bloom (DAFB), which gradually increased during the course of the experiment
Summary
Apple production is a major horticultural sector with 87 million tons produced in 2019 (FAOSTAT, https://www.fao.org/home (accessed on 23 November 2021)). Russeting detracts from fruit appearance, manifesting brownish rough corky texture on the fruit surface [1], leading to reduced market value and profitability on fruit production. Environmental stresses were one of the first characterized causes associated with russeting in apples [2,3]. Russeting seems to be initiated at the early stages of fruit development: the extreme mechanical tension on the fruit surface during this time of rapid growth seems to predispose apple fruit skin to cuticle microcracking [4]. Histological studies performed on apples revealed that cuticle thickness seemed to be inversely correlated with the appearance of russeting [5]. Russeted apple skin displayed a lower expression of genes linked to cuticle biosynthesis, and regulation was associated with a decreased content of cuticle monomers [5,6,7]
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