Melon ethylene-mediated transcriptome and methylome dynamics provide insights to volatile production

Abstract

16During climacteric ripening large-scale transcriptional modifications are governed by ethylene. While 17 ripening-related chromatin modifications are also known to occur, a direct connection between these 18 factors has not been demonstrated. We characterized ethylene-mediated transcriptome modification, 19 genome methylation dynamics, and their relation to organoleptic modifications during fruit ripening in the 20 climacteric melon and an ethylene repressed line where the fruit-specific ACC oxidase 1 (ACO1) gene 21 was targeted by antisense. The ACO1 antisense line exhibited mainly reduced transcriptional repression of 22 ripening-related genes associated with DNA CHH hypomethylation at the onset of ripening. Additionally, 23 transcription of a small set of ethylene-induced genes, including known ripening-associated genes, was 24 inhibited by ACO1 repression and this inhibition was associated with CG hypermethylation. In the ACO1 25 antisense line, the accumulation of aromatic compounds, which are mainly derived from the catabolism of 26 amino acids, is known to be inhibited. One of the ethylene-mediated transcriptionally up-regulated genes, 27CmTHA1, encoding a threonine aldolase, exhibited differential cytosine methylation. Threonine aldolase 28 catalyzes the conversion of L-threonine/L-allo threonine to glycine and acetaldehyde and thus is likely 29 involved in threonine-dependent ethyl ester biosynthesis. Yeast mutant complementation and incubation 30 of melon discs with labeled threonine verified CmTHA1 threonine aldolase activity, revealing an 31 additional ethylene-dependent amino acid catabolism branch involved in climacteric melon ripening. 32 33 2

Melon Genetic Resources Characterization for Rind Volatile Profile

“…The melon flesh volatile profile has already been deeply studied, basically in commercial genotypes, but also including a few representatives of other horticultural groups [9,[11][12][13][14][15][16][17][18][19][20][21], and the comprehension of the pathways and genes involved in their biosynthesis is currently being prompted using genomic, transcriptomic and biochemical approaches and also segregating populations [22][23][24][25][26][27][28]. Recently, the flesh aroma profile of a melon core collection of 71 accessions representing the whole species diversity has been analyzed [5].…”

CRISPR/Cas9 gene editing uncovers the roles of CONSTITUTIVE TRIPLE RESPONSE 1 and REPRESSOR OF SILENCING 1 in melon fruit ripening and epigenetic regulation

“…S3), suggesting that more than one DNA demethylase may be involved in this process. Moreover, a recent study showed hypomethylation of ethylene induced genes at 30 DAP in a climacteric variety, suggesting the important role of DNA demethylases during melon ripening (Feder et al, 2020).…”

“…Recent studies demonstrated that DNA methylation levels play an important role at the onset of fruit ripening in tomato (Zhong et al, 2013). Moreover, the DNA methylation dynamics in a climacteric and an ethylene repressed line have been recently studied in melon (Feder et al, 2020). Modulation of DNA methylation levels is governed by DNA methylases and demethylases.…”

Evidence Supporting a Role of Alternative Splicing Participates in Melon (Cucumis melo L.) Fruit Ripening

“…Notably, MELO3C014437 (CmACO1), MELO3C009845 (CmCGS), MELO3C010776 (CmBCAT1), and MELO3C023371 (CmGKC) showed high expression levels in CM (Figure 1g). CmACO1, associated with ripening and ethylene biosynthesis [35][36][37], and CmCGS, a regulator of ethylene synthesis biochemical flux and SAM production [38], may contribute to reduced methylation in ACO1 antisense fruit. Additionally, ETH may control the synthesis of volatile aromatic and methyl-branched molecules through the relative expression of CmBCAT1, which catalyzes enhanced AT activity [39].…”