Effects Of Exogenous Methyl Jasmonate On The Growth And Oil Biosynthesis Of Camellia Oleifera Fruits

Camellia oleifera Abel.is an important woody edible oil tree species in China.It plays an important role in maintaining national grain and oil security,developing green economy and increasing farmers’ income in mountainous areas.However,low yield and unstable quality have plagued the healthy development of C.oleifera industry for a long time.The growth and development of C.oleifera fruits are directly related to its yield and quality.However,the research foundation on how to regulate the growth of C.oleifera fruit and improve its yield and quality through plant growth regulators is poor.In this study,excellent variety of ’C.oleifera Huashuo’ approved by the state was used as test materials,and different concentrations of exogenous Methyl Jasmonate(MeJA)were sprayed.Phenotypic traits,oil accumulation and fatty acid compositions of C.oleifera seeds treated with different concentrations were compared.After selecting the optimal concentration,transcriptomic analysis was carried out to identify differential genes of MeJA regulating oil anabolism.The purpose of this study was to provide scientific basis for the application of this growth regulator to improve the yield and quality of C.oleifera.The main results were as follows:1.Low concentration exogenous MeJA treatment promoted the growth of C.oleifera fruits.In the process of C.oleifera fruits development,the fresh fruit weight showed a single S-shaped curve,horizontal diameter and vertical diameter showed double S-shaped curve.In general,the fresh fruit weight,horizontal diameter and vertical diameter of fruits after treated with exogenous MeJA showed the effects of low concentration promotion and high concentration inhibition.When the fruit matured(October 24),the fresh fruit weight of 0.1 mmol·L-1 and 0.5 mmol·L-1 MeJA treatment increased significantly by 35.61%and 41.10%compared with the control group,respectively.Compared with the control group,the horizontal diameter increased by 16.13%and 10.26%,respectively.In the process of fruit development,the peel thickness increased after 0.1 mmol·L-1 and 0.5 mmol·L-1 MeJA treatment,but there was no significant difference among the treatments when the fruit was mature.In addition,the effect of treating C.oleifera fruit with SHAM was unstable.2.Low concentration exogenous MeJA treatment promoted oil accumulation and fatty acid component changes of C.oleifera seeds.After treated with different concentrations of MeJA,it was shown that low concentration promoted oil accumulation in C.oleifera seeds,while high concentration inhibited it.Specifically,the oil content increased most significantly after 0.5 mmol·L-1 MeJA treatment,while the oil accumulation was inhibited significantly after 5 mmol·L-1 MeJA treatment.When C.oleifera fruits matured(October 24),the oil content of seeds treated with 0.5 mmol·L-1 MeJA increased by 43.07%compared with the control group.In addition,it was found that the morphological changes of oil bodies in seed kernel cells after 0.5 mmol·L-1 MeJA treatment were the same with the control group,but the number of oil bodies increased significantly.After 0.5 mmol·L-1 MeJA treatment,the relative content of oleic acid increased significantly in August and was slightly higher than CK at maturity,while 5 mmol·L-1 MeJA treatment significantly inhibited the relative content of oleic acid.Similar to the change of the relative content of oleic acid,the relative content of unsaturated fatty acids after 0.5mmol·L-1 MeJA treatment was significantly promoted in August.Additionly,the effect of SHAM was unstable.3.Transcriptomic analysis of C.oleifera seeds after treated with 0.5 mmol·L-1 MeJA.Based on the changes of phenotypic characters,oil accumulation and fatty acid compositions of C.oleifera seeds,0.5 mmol·L-1 MeJA was selected as the optimum concentration.Then,transcriptome sequencing was carried out with seeds at three different developmental stages after 0.5 mmol·L-1 MeJA treatment.The results showed that after 0.5 mmol·L-1 MeJA treatment,184 differentially expressed genes(DEGs)of CK1 vs J1(initial stage of oil biosynthesis)were up-regulated and 178 DEGs were down regulated.CK2 vs J2(peak of oil biosynthesis)were up-regulated 512 DEGs and down regulated 849 DEGs.CK3 vs J3(seed maturity)were upregulated 603 DEGs and down regulated 788 DEGs.Through KEGG(Kyoto Encyclopedia of genes and genes)enrichment analysis,a total of 11 pathways involving lipids in all pathways enriched by DEGs,including α-linolenic acid metabolism,linoleic acid metabolism,unsaturated fatty acid biosynthesis,glycerol ester metabolism,fatty acid elongation,fatty acid metabolism,glycerol phospholipid metabolism,ether lipid metabolism,pantothenic acid and coenzyme A biosynthesis,fatty acid biosynthesis and fatty acid degradation pathway.Sixty related genes were screened,including ACC,BCCP,DGAT,LACS,GPAT,FAD,SAD,LOX,FAT and fadD.Among them,FAD gene has the largest number with 12,and 8 genes such as ACC1,SAD6,FAD2 and LACS4-3 were significantly up-regulated after exogenous MeJA treatment compared with control group,which was speculated to be the important genes to promote oil biosynthesis after MeJA treatment.