Comparative study on fruit development and oil synthesis in two cultivars of Camellia oleifera

Abstract

Background: The oil-tea tree (Camellia oleifera Abel.) is a woody tree species that produces edible oil in the seed. C. oleifera oil has high nutritional value and is also an important raw material for medicine and cosmetics. In China, due to the uncertainty on maturity period and oil synthesis mechanism of many C. oleifera cultivars, growers may harvest fruits prematurely, which could not maximize fruit and oil yields. In this study, our objective was to explore the mechanism and differences of oil synthesis between two Camellia oleifera cultivars for a precise definition of the fruit ripening period and the selection of appropriate cultivars.

Results: The results showed that 'Huashuo' had smaller fruits and seeds, lower dry seed weight and lower expression levels of fatty acid biosynthesis genes in July. We could not detect the presence of oil and oil bodies in 'Huashuo' seeds until August, and oil and oil bodies were detected in 'Huajin' seeds in July. Moreover, 'Huashuo' seeds were not completely blackened in October with up to 60.38% of water and approximately 37.98% of oil in seed kernels whose oil content was much lower than normal mature seed kernels. The oil bodies in seed endosperm cells of 'Huajin' were always higher than those of 'Huashuo' from July to October.

Conclusion: Our results confirmed that C. oleifera 'Huashuo' fruits matured at a lower rate compared to 'Huajin' fruits and that 'Huajin' seeds entered the oil synthesis period earlier than 'Huashuo' seeds. Moreover, 'Huashuo' fruits did not mature during the Frost's Descent period (October 23-24 each year).

Keywords: Camellia oleifera Abel; Fatty acid; Fruit development; Nutrient content; Oil body observation; Transcriptome.

Fig. 1

Camellia oleifera ‘Huashuo’ and ‘Huajin’ cultivars and their fruit development. A Tree body of C. oleifera ‘Huashuo’. B Fruits of C. oleifera ‘Huashuo’. C Tree body of C. oleifera ‘Huajin’. D Fruits of C. oleifera ‘Huajin’. E Fruit development in C. oleifera ‘Huashuo’ in July. F Fruit development in C. oleifera ‘Huashuo’ in August. G Fruit development in C. oleifera ‘Huashuo’ in September. H Fruit development in C. oleifera ‘Huashuo’ in October. I Fruit development in C. oleifera ‘Huajin’ in July. J Fruit development in C. oleifera ‘Huajin’ in August. K Fruit development in C. oleifera ‘Huajin’ inSeptember. L Fruit development in C. oleifera ‘Huajin’ in October. (1) Whole fruits of C. oleifera. (2) Cross-sections of C. oleifera fruit. (3) Seeds of C. oleifera. Scale bars, 10 mm

Fig. 2

Nutrient contents in seeds of Camellia oleifera ‘Huashuo’ and ‘Huajin’ cultivars. Different uppercase and lowercase letters indicate significant differences (P ≤ 0.05; Duncan’s multiple range tests) between cultivars and periods, respectively. Vertical bars indicate standard errors (SEs) of the mean (n = 3)

Fig. 3

Relative fatty acid contents in seeds of Camellia oleifera ‘Huashuo’ and ‘Huajin’ cultivars. Different uppercase and lowercase letters indicate significant differences (P ≤ 0.05; Duncan’s multiple range test) between cultivars and periods, respectively. Vertical bars indicate SEs of the mean (n = 3)

Fig. 4

Oil bodies in Camellia oleifera ‘Huashuo’ and ‘Huajin’ cultivars as observed using laser-scanning confocal microscopy. Oil bodies in (A) July, (B) August, (C) September and (D) October. (1) Oil-body-stained images. (2) White-light images. (3) Merged images. Scale bars: 10 μm. CW, cell walls; OB, oil bodies

Fig. 5

Oil bodies in Camellia oleifera ‘Huashuo’ and ‘Huajin’ cultivars as observed using transmission electron microscopy. Oil bodies in (A) C. oleifera ‘Huashuo’ and (B) C. oleifera ‘Huajin’. Oil bodies in (1) July, (2) August, (3) September and (4) October. Scale bars: (1–3) 2 μm; (4) 10 μm. CW, cell walls; PM, plasm membrane; OB, oil bodies

Fig. 6

Differentially expressed genes (DEGs) in Camellia oleifera ‘Huashuo’ and ‘Huajin’ cultivars and Gene Ontology (GO) functional annotation at different development periods. A Number of up/down-regulated DEGs at each developmental stage. B Venn diagram showing the DEGs shared among the four gene sets. C GO classification. A1-B1, C. oleifera ‘Huajin’ seeds in July vs. C. oleifera ‘Huashuo’ seeds in July; A2-B2, C. oleifera ‘Huajin’ seeds in August vs. C. oleifera ‘Huashuo’ seeds in August; A3-B3, C. oleifera ‘Huajin’ seeds in September vs. C. oleifera ‘Huashuo’ seeds in September; A4-B4, C. oleifera ‘Huajin’ seeds in October vs. C. oleifera ‘Huashuo’ seeds in October

Fig. 7

Map showing patterns of expression for fatty acid-biosynthesis genes. Expression levels of each gene were shown by heatmap using log₁₀(FPKM). A1, C. oleifera ‘Huajin’ seeds in July; B1, C. oleifera ‘Huashuo’ seeds in July; A2, C. oleifera ‘Huajin’ seeds in August; B2, C. oleifera ‘Huashuo’ seeds in August; A3, C. oleifera ‘Huajin’ seeds in September; B3, C. oleifera ‘Huashuo’ seeds in September; A4, C. oleifera ‘Huajin’ seeds in October; B4, C. oleifera ‘Huashuo’ seeds in October