| Artemisia sphaerocephala,a superdry perennial semi-shrub,is an important member belonging to the Artemisia genus of the Compositae family,and one of the pioneer species for windbreak and sand fixation in the arid desert area of Northwest China(Flora of China,1991).Artemisia sphaerocephala seeds contain 31.96%oil and are rich in linoleic acid(C18:2)and tocopherols,however,the formation mechanism and their regulatory relationship of related traits during seed development are still unknown.In this study,A.sphaerocephala seeds at seven different development stages at 10,20,30,40,50,60,and 70 days after flowering(designated as S1?S7),respectively,were employed as experimental samples,the accumulation patterns of lipid,fatty acids,and tocopherols during seed development were studied using high resolution mass spectrometry,gas chromatography-mass spectrometry and high performance liquid chromatography,respectively.The regulatory network for the biosynthesis of related traits were constructed by 2+3 combined transcriptome sequencing,and the transcriptional regulation mechanism of lipid,fatty acids and tocopherol formation during seed development of A.sphaerocephala were preliminary elucidated.This study will lay the foundation for the in-depth exploration of the excellent quality traits of desert plants,and provide excellent genetic resources for forage quality breeding,simultaneously.The main conclusions are as follows:(1)A total of 206 lipids,including 101 glycerophospholipids,63 glycerides,26glyceroglycolipids and 16 lysophospholipids,were detected during the seed development of A.sphaerocephala.Triacylglycerols(TAG)in the glycerides was the main component of the lipids of A.sphaerocephala seeds,accounting for 69.72%?98.19%of the total lipids,and the main species were 52:3,52:2,52:4,50:1 and 54:6;Followed by 16 lysophospholipids,accounting for 1.08%?21.88%of total lipid;Then,101 glycerophospholipids,the content of the six main glycerophospholipids were in descending order:phosphatidic acid(PA)>phosphatidylcholine(PC)>phosphatidylinositol(PI)>phosphatidylethanolamine(PE)>phosphatidylglycerol(PG)>phosphatidylserine(PS),and the main species of the first four glycerophospholipids are34:2 and 36:4;The content of the two main glyceroglycolipids was digalactosyldiacylglycerol(DGDG)>monogalactosyldiacylglycerol(MGDG),and the main species were 36:6,36:4 and 38:6.The gene analysis of lipid biosynthesis showed that phospholipid:diacylglycerol acyltransferase(PDAT)and acyl?Co A:diacylglycerol acyltransferase(DGAT)synergistically regulated the TAG biosynthesis of A.sphaerocephala seeds.(2)The oil content continued to rise from 10.12%at 10 days after flowering to31.96%at the mature stage,and the maximum accumulation was in the S1?S2 period.C18:2 accounted for 80.62%of the total fatty acids.The transcription factors FUS3 and b HLH played a critical role in the seed oil biosynthesis.The high expression of related genes involved in fatty acid and TAG biosynthesis in S1?S2 was an important reason for the rapid accumulation of oil in the early stage.The perfect harmonization of the high expression of gene encoding oleate desaturase(FAD2)with the extremely low expression of gene encoding linoleate desaturase(FAD3)regulated the accumulation of C18:2.(3)The total tocopherol content of A.sphaerocephala seeds was 114.65?g g-1 FW.?-toc was the main form,and its content increased continuously from 7.71?g g-1 FW to 98.50?g g-1 FW with the seeds development,and had the largest accumulation rate in S2?S3.Tocopherol biosynthesis was co-regulated by precursor pathways(shikimate pathway and mon-mevalonate pathway)and core pathway genes.The high expression of genes encoding 2-methyl-6-phytyl benzoquinone methyltransferase and?-tocopherol methyltransferase(VTE3 and VTE4)as well as the low expression of genes encoding tocopherol cyclase(VTE1)in the core pathway jointly promoted the high accumulation of?-toc.Moreover,the regulation of high?-tocopherol on FAD2,DGAT2 and PDAT may be one of the reasons for the high accumulation of C18:2. |
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