Physiological, Histological, and Molecular Analyses of Avocado Mesocarp Fatty Acids During Fruit Development

Abstract

Fatty acids are important components of the avocado mesocarp, so a better understanding of how their change during fruit development will contribute to improving the quality of avocado fruits and their nutritional value. The changes in fatty acids, lipid droplets, and expression of some key genes and regulators participating in late glycolysis and fatty acid biosynthesis were analyzed at different stages of the development of avocado mesocarp. The total fatty acid contents of the avocado mesocarp increased during fruit development, with an increase by a factor of seven (from 1,628.04 to 11,116.30 mg/100 g dry weight) in the late stage of fruit maturation, this was confirmed by the changes observed in the lipid droplets. The composition of the main fatty acids varied at four developmental stages of fruit development. Palmitic, palmitoleic, oleic, and linoleic acid contents generally increased during fruit development, reaching maxima at Harvest, with percentages of total fatty acids of 50%, 9%, 31%, and 8%, respectively. Meanwhile, the amount of PaWRI1, PaACP4-2, and PapPK-β1 expressed consistently increased by up to 4-fold during fruit development. This comprehensive analysis has indicated that the changes in the expressions of PaWRI1, PaACP4-2, and PapPK-β1 were consistent with those in the total fatty acid contents, so they might have key roles in the accumulation of oil in the avocado mesocarp.

Primary Metabolism in Avocado Fruit

“…From 65 to 125 DAP, PaWRI1, PaACP4-2, and PapPK-β1 displayed a fourfold increase but kept showing significant differences among the four stages of fruit development but PaACP4-1 only increased 0.5–1.0-fold expression at 65 DAP and 1.42 fold at 125 DAP. Thus, the observed total fatty acid changes during the four stages of avocado fruit development by Ge et al (2019) were consistent with the changes of expression of PaWRI1, PaACP4-2, and PapPK-β1 but inconsistent with PaACP4-1 and PaWRI2 expression patterns.…”

“…In contrast to the role of WRI2 in Arabidopsis fatty acid biosynthesis, the high expression of this ortholog in avocado mesocarp during oil accumulation suggests a potential role in TAG accumulation in avocado. Ge et al (2019) recently reported that while PaWRI1, PaACP4-1, and PapPK-β1 seem to play key roles in the accumulation of oil in avocado mesocarp as also reported by Kilaru et al (2015), the pattern of expression of PaWRI2 differed indicating that this transcription factor contrary to what was reported by Kilaru et al (2015) might not be influencing oil accumulation.…”

“…These proteins are supposed to bind and stabilize lipid particles in avocado mesocarp. Recently, Ge et al (2019) reported a histological analysis of lipid droplets in avocado mesocarp during fruit development (from 65 days after pollination, DAP to 125 DAP for the avocado variety Guitenda N°2, Persea americana var. guatemalensis).…”

“…The lipid composition agreed with the higher expression levels of LPCAT (lysophosphatidylcholine acyltransferase) and PDAT (phospholipid:diacylglycerol acyltransferase) in stages I–III compared to IV and V. Thus, a possible role for acyl editing during early stages of development is proposed and supported by higher levels of transcripts for an ortholog of oleate desaturase (FAD2) during early stages of development (I–III) compared to IV and V respectively. Recently, Ge et al (2019) reported the fatty acid mesocarp composition during four stages of avocado fruit development (65–125 DAP; corresponding to 9.45–54.75 g of mesocarp mass) and the expression of key genes and regulators of glycolysis and fatty acid biosynthesis. The composition of fatty acids varied at the four stages of development.…”

Genome-Wide Mapping of Histone H3 Lysine 4 Trimethylation (H3K4me3) and Its Involvement in Fatty Acid Biosynthesis in Sunflower Developing Seeds

“…WRI1 belongs to the APETALA 2 transcription factor family and is a regulator of plant oil biosynthesis [ 25 ]. Although WRI1 has been described and functionally characterized in different plants, including Brassica napus , Camelina sativa , Persea americana , Ricinus communis , and Jatropha curcas [ 75 , 76 , 77 , 78 , 79 ], among other species, the function of WRI1 in sunflower seeds is not well characterized. WRI1 is regulated, as described above, by LAFL transcription factors.…”