Proteome Landscape during Ripening of Solid Endosperm from Two Different Coconut Cultivars Reveals Contrasting Carbohydrate and Fatty Acid Metabolic Pathway Modulation

Abstract

Cocos nucifera L. is a crop grown in the humid tropics. It is grouped into two classes of varieties: dwarf and tall; regardless of the variety, the endosperm of the coconut accumulates carbohydrates in the early stages of maturation and fatty acids in the later stages, although the biochemical factors that determine such behavior remain unknown. We used tandem mass tagging with synchronous precursor selection (TMT-SPS-MS3) to analyze the proteomes of solid endosperms from Yucatan green dwarf (YGD) and Mexican pacific tall (MPT) coconut cultivars. The analysis was conducted at immature, intermediate, and mature development stages to better understand the regulation of carbohydrate and lipid metabolisms. Proteomic analyses showed 244 proteins in YGD and 347 in MPT; from these, 155 proteins were shared between both cultivars. Furthermore, the proteomes related to glycolysis, photosynthesis, and gluconeogenesis, and those associated with the biosynthesis and elongation of fatty acids, were up-accumulated in the solid endosperm of MPT, while in YGD, they were down-accumulated. These results support that carbohydrate and fatty acid metabolisms differ among the developmental stages of the solid endosperm and between the dwarf and tall cultivars. This is the first proteomics study comparing different stages of maturity in two contrasting coconut cultivars and may help in understanding the maturity process in other palms.

Untargeted Metabolomics Analysis of Liquid Endosperm of Cocos nucifera L. at Three Stages of Maturation Evidenced Differences in Metabolic Regulation

“…The metabolome of the Yucatan green dwarf coconut is highly conserved with metabolomes reported for COD and MYD dwarf varieties from India, with respect to sugars, organic acids, and amino acid accumulation [4], and is consistent with the recently reported proteomics study for green dwarf coconut [49], although some discrepancies were also noted.…”

“…A key enzyme in the glyoxylate cycle is isocitrate lyase (ICL), which catalyzes the cleavage of isocitrate into glyoxylate and succinate; succinate enters the mitochondria for subsequent reactions [57]. Félix et al [49] recently demonstrated that glyoxylate is significantly regulated during the ripening of coconut fruits, following an inverted bell curve, in agreement with the regulation of glycolysis. Glyoxylate and dicarboxylate metabolisms are also related to abiotic stress, providing a balance in metabolic changes to improve tolerance to drought stress [37].…”

“…The classification of fruits in different stages of maturity is based on phenotypic characteristics; although this classification has worked quite well overall, some scatter in the PCA analyses show that there is some bias in the classification of the samples [4,49]. Kumar et al [4] proposed eight biomarkers for the different stages of maturity which were identified when they conducted targeted nutritional metabolomics.…”