Studies On The Characteristics Of Fruit Development And The Regulation Mechanism Of MeJA In Camellia Oleifera

Camellia oleifera Abel.(C.oleifera)is an important woody edible oil species in China and the fruit development is directly related to yield and quality of C.oleifera.In this study,the C.oleifera cultivar ’Huashuo’ was used as the research material,the characteristics of fruit growth and development and the accumulation of substances,the influence of exogenous hormones,and the molecular mechanism of methyl jasmonate regulating the seed development of ’Huashuo’ were investigated systematically at the phenotypic observation,physiological level,cell level,and molecular level using field experiment observation,histological microscopic analysis,hormone analysis,transcriptome and metabolome analysis,and gene interaction verification.The aim of this study was to reveal the growth and development characteristics of ’Huashuo’ fruit and the hormone regulation mechanism,which provide scientific basis for artificial regulation of C.oleifera fruit development to improve its yield and quality.The main results were as follows:1.The characteristics of fruit growth and development and the accumulation of substances in ’Huashuo’ fruits were identified.The characteristics of fruit growth and development and the accumulation of substances in ’Huashuo’ fruits were studied using field experiment observation,histological microscopic analysis,chromatographic analysis and metabolome.The results showed that the growth curve of ’Huashuo’ fruit horizontal diameter and vertical diameter,fruit weight and fresh seed weight belonged to "S" type.Specifically,they increased rapidly at 170 DAP(day after pollination)and stabilized at 292 DAP,the shell thickness continued to thicken from 170 DAP to 228 DAP and then slowly thinning until the fruit matured.The cotyledon-shaped embryo of ’Huashuo’ seeds was formed at 235 DAP.At this time,the endosperm was gradually disintegrate,and the kernel gradually developed from translucent,loose and uncompact state to milky white or lightyellow mature kernel.The oil content increased significantly with the maturity of ’Huashuo’seeds,especially from 292 DAP,and oil bodies accounted for about 1/3 of the whole cells at the maturity of seeds.A total of 433 metabolites were identified from ’Huashuo’ seeds,of which 34.18%(148 metabolites)were flavonoid compounds,which were mainly enriched in the seed coat.The contents of endogenous AB A,GA3,IAA,ZT,MeJA and MT significan-tly increased from 170 DAP and reached the peak at 258 DAP but then decreased in seed,which consistent with the stage of rapid fruit expansion and shell thinning,suggesting that these hormones might affect the development process of‘Huashuo’fruit.2.The plant prowth regulators to promote the growth and development of C.oleifera fruits were found.Six plant growth hormones with different concentrations of 6BA,ABA,GA3,IAA,MeJA,and MT were used to treat whole C.oleifera trees,respectively.The results showed that the different exogenous hormone treatments had different effects on fruit development of C.oleifera,among which 0.5 mmol/L MeJA significantly increased the fresh fruit weight,seed size,and seed weight at maturity stage about by 41.1%,29.13%,and 31.81%,respectively.Moreover,the larger seeds induced by 0.5 mmol/L MeJA resulted from more cell numbers and larger cell area in the out-seed coat at early development stage(124 to 236 DAP)and embryo(236 to 334 DAP).Interestingly,0.5 mmol/L MeJA treatment significantly increased the number of oil bodies,oil content and relative contents of unsaturated fatty acids,but reduced the relative content of saturated fatty acid in C.oleifera seeds.At 250 DAP,0.5 mmol/L MeJA treatment significantly increased flavonoid content by 33.46%and flavonoid was highly enriched in the seed coat,mainly distributed near the cell wall.Therefore,exogenous 0.5mmol/L MeJA was an important plant prowth regulators affecting the growth and development,and accumulation of substance of C.oleifera fruit.3.The molecular mechanism of MeJA regulating seed growth and development of C.oleifera was elucidated.Baed on the transcriptome analysis and gene interaction verification,we found that the valuable different expressed genes(DEGs)responded to MeJA mainly participated in the processing of cell wall development,unsaturated fatty acids,and flavonoid compounds biosynthesis.During seed development,important genes related to signal pathways that control seed size,as well as cell proliferation and expansion were identified and MeJA could regulate the expression of positive or negative actors in these pathways,as well as cell proliferation and cell expansion,resulting in larger seeds.Acetylco carboxylase(ACCase)and biotin carboxylcarrier protein of acetyl-CoA carboxylase 2(BCCP2)were important regulatory genes for oil accumulation,and their expressions were significantly up-regulated by MeJA.Stearoyl-acp desaturase(SAD)and fatty acid desaturase(FAD)were key genes in the biosynthesis of unsaturated fatty acids.After 0.5 mmol/L MeJA treatment,the expression levels of SAD6-1 and SAD6-2 were increased by more than 90%,while the expression level of FAD2-3 was decreased by about 56.41%,compared with control.A total of 48 structural genes related to flavonoid biosynthesis were significantly regulated by MeJA,among which ANS,ANR2 and UGT71K1 were the hub genes responding to MeJA regulation.Based on the weighted correlation network analysis,yeast one-hybrid assay,electrophoretic mobility shift assay,and dual-Luciferase assay,the results showed that CoMYC2,an important switch gene of MeJA signaling pathway,positively regulated the transcription of important genes related to seed size promotion(CoCDKB2-2,CoCYCB2-3,and CoXTH9),oil accumulation(CoACC1),and flavonoid biosynthesis(CoANS and CoANR2),while inhibited the transcription of CoFAD2-3.