Abstract
Green-colored fiber (GCF) is the unique raw material for naturally colored cotton textile but we know little about the pigmentation process in GCF. Here we compared transcriptomes and metabolomes of 12, 18 and 24 days post-anthesis (DPA) fibers from a green fiber cotton accession and its white-colored fiber (WCF) near-isogenic line. We found a total of 2047 non-redundant metabolites in GCF and WCF that were enriched in 80 pathways, including those of biosynthesis of phenylpropanoid, cutin, suberin, and wax. Most metabolites, particularly sinapaldehyde, of the phenylpropanoid pathway had a higher level in GCF than in WCF, consistent with the significant up-regulation of the genes responsible for biosynthesis of those metabolites. Weighted gene co-expression network analysis (WGCNA) of genes differentially expressed between GCF and WCF was used to uncover gene-modules co-expressed or associated with the accumulation of green pigments. Of the 16 gene-modules co-expressed with fiber color or time points, the blue module associated with G24 (i.e., GCF at 24 DPA) was of particular importance because a large proportion of its genes were significantly up-regulated at 24 DPA when fiber color was visually distinguishable between GCF and WCF. A total of 56 hub genes, including the two homoeologous Gh4CL4 that could act in green pigment biosynthesis, were identified among the genes of the blue module that are mainly involved in lipid metabolism, phenylpropanoid biosynthesis, RNA transcription, signaling, and transport. Our results provide novel insights into the mechanisms underlying pigmentation of green fibers and clues for developing cottons with stable green colored fibers.
Highlights
Colored cottons (NCCs) are varieties of cotton that produce fibers with non-white colors [1]
Several genes of the pathway that are related to pigment synthesis have been identified and characterized, such as genes encoding chalcone synthases (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylases (F3H), flavonoid 3, 5 -hydroxylases (F3 5 H), dihydroflavonol 4-reductases (DFR), leucoanthocyanidin reductases (LAR), anthocyanidin synthase (ANS), and anthocyanidin reductases (ANR) [4,8,9]
To compare green-colored fibers (GCF) and white-colored fiber (WCF) metabolites, datasets obtained from quadrapole time of flight–mass spectrometry (QTOF–MS) by electrospray ionization (ESI+ and ESI–) were subjected to principal component analysis (PCA)
Summary
Colored cottons (NCCs) are varieties of cotton that produce fibers with non-white colors [1]. The main pigment components in the brown-colored fiber (BCF) are proanthocyanidins or their derivatives generated from the flavonoid pathway. The pigment components of the green-colored fibers (GCF) are more complex than that of BCF. The unidentified components of the wax could be separated into a colorless fluorescent fraction, and a yellow-pigmented fraction. Two caffeic-acid derivatives have been isolated from the yellow components of the GCF extract [1,16]. Caffeic acid derivatives are produced by the phenylpropanoid biosynthesis pathway. When the enzymatic activity of phenylalanine ammonia lyase (PAL) is inhibited, in vitro cultured fibers from ovules of GCF variety remained white, and the colorless caffeic-acid derivatives and yellow components could no longer be detected [14]. Zhao and Wang [18] reported that the contents of flavonoids, including flavone and flavanols, were higher in GCF than in WCF
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