Identification And Expression Analysis Of The NF-Y Gene Family In Olive

Olive(Olea europaea L.)is a famous oil and fruit tree species.Its fresh fruit cold pressed olive oil is in high demand due to its high content of beneficial unsaturated fatty acids and bioactive components.However,domestic olive oil production is currently low and of poor quality and is still dependent on imports.Therefore,expanding domestic olive cultivation area,increasing production and improving olive oil quality have been in urgent needs for the development of Chinese olive oil.The nuclear factor Y(NF-Y)family is a typical transcription factor family in eukaryotes,and its members can affect plant seed maturation and oil synthesis by influencing abscisic acid(ABA)synthesis and signal transduction.However,there is few studies on the regulation of oil synthesis in olive by NFY gene family,especially the transcriptional regulation mechanism.Therefore,in this study,the whole genome data of olive were used to obtain NF-Y gene family members,and their structural characteristics and evolutionary relationships were analyzed.On this basis,quantitative real-time PCR was performed to determine the expression level of candidate OeNF-Y gene during the development of olive fruit,and its correlation with olive oil content and fatty acid composition.Finally,ABA was used as inducer to study its effect on the regulation of candidate OeNF-Y gene expression.This will lay the foundation for further study on transcriptional regulation of OeNF-Y gene family in olive oil synthesis.The main research results are as follows:(1)Bioinformatics analysis of the olive NF-Y gene family: 50 OeNF-Y family members were identified from the whole genome of olive based on hidden markov model,and were divided into three groups according to cluster analysis: OeNF-YA(16),OeNF-YB(24)and OeNF-YC(10).The amino acid number,molecular weight and isoelectric point of NF-Y family members of olive are 50～770 aa,5.47～85.34 k Da and 4.69～9.93 respectively,with most being hydrophilic proteins.Structural analysis shows that most olive NF-Y genes are structurally conserved.Protein function prediction results showed that the presumed homolog of OeNF-YB19 was L1 L,which plays an important role in Arabidopsis seed development,fatty acid synthesis and ABA response.Evolutionary pattern analysis showed that three pairs of OeNF-Y genes were involved in tandem duplication,and 17 genes were involved in 15 segmental duplication,suggesting that segmental duplication was the main factor in the expansion of OeNF-Y gene family.OeNF-Y gene has high collinearity with dicotyledonous plants such as cocoa and grape,but low collinearity with monocotyledonous plants such as rice,indicating that OeNF-Y gene has strong homology among dicotyledonous plants.Analysis of the cis-acting elements showed that 25 cis-acting elements were found in the 1.5 kb region upstream of OeNF-Y gene,including the core elements of NF-Y,CCAAT box,5 growth and development regulatory elements,5 light response elements,4 stress response elements,and 10 hormone response elements.Eight genes contain ABA response element,OeNF-YA1/A8/A13/B7/B9/B20/B21/C6,were selected to explore the effects of exogenous ABA induction on their expression.(2)Screening of candidate OeNF-Y gene for regulating oil synthesis: Both varieties have a fruit oil content of around 40% at maturity.The results of GC-MS analysis showed that the oil contained six fatty acids: palmitic acid(11.12%-18.74%),palmitoleic acid(0.09%-2.20%),oleic acid(67.66%-75.10%),linoleic acid(1.13%-4.44%),stearic acid(2.03%-2.95%)and Arachidonic acid(0.05%～0.18%).Transcriptome data and q PCR expression profiles showed that OeNF-Y genes were differentially expressed in pedicels,leaves,fruits and roots in July and November,with nine genes,OeNFYA2/A12/B7/B10/B16/B19/C1/C2/C8,being highly expressed in fruits.Correlation analysis showed that OeNF-YA12 was negatively correlated with olive oil content(r=-0.724),OeNFYA2 was positively correlated with linoleic acid content(r=0.722),and OeNF-YA12 was negatively correlated with palmitoleic acid(r=-0.724).Combined with the results of bioinformatics analysis,three genes,OeNF-YA2/A12/B19,were screened out to be involved in the regulation of olive oil synthesis and verified by exogenous ABA induction test.(3)Analysis of exogenous ABA induction: Take the two varieties together,four genes,OeNF-YA2/A8/B7/B19,were up-regulated,OeNF-YA1 was down-regulated,OeNF-YB21 was not induced and five genes,OeNF-YA12/A13/B9/B20/C6,were differently induced in the fruit of the two varieties.Compared to the control group,the olive oil and linoleic acid content in the ABA experimental group increased by 1.52%-2.59% and 0.26%-0.6%respectively.In conclusion,OeNF-YA2/B19 transcription factor plays a potential regulatory role in olive oil synthesis,exogenous ABA can up-regulate the expression of OeNF-YA2/B19 gene and increase olive oil content and linoleic acid content.These results indicated that OeNFYA2/B19 gene may positively regulate olive oil synthesis through ABA signaling pathway.