Transcriptome Analysis Of Carrot Petaloid Cytoplasmic Male Sterile And Maintainer Line

Carrot petaloid CMS line is the main application type used for cross breeding in carrot,which is of important application value.This CMS type is caused by the conversion of stamen into petal-like structure during flower development.Thus,petaloid CMS is not only an ideal model for studying the interaction of nucleus and cytoplasm,but also an important material for studying the homeotic organ alternation of flowers.However,for a long time,the research on carrot CMS mainly focused on mitochondrial genes and there were few studies on the nuclear genes.So far,the CMS has not been studied from the overall level and the molecular mechanism of CMS is still unclear.In this study,the carrot petaloid type CMS(P2S)and its maintainer line(P2M)were used as materials.Firstly,we observed the flower development process of umbels from P2 S and P2 M at four different developmental stages(T1-T4)by scanning electron microscopy.Then,we conducted transcriptome analysis between the petaloid CMS line and its maintainer line at four flower developmental stages and preliminary analysis the molecular mechanism of carrot petaloid CMS on a global level.The observation results by SEM revealed that only one shoot apical meristem germinated in the middle of the stem apex at T1.During T2,some young inflorescence appeared at the periphery of the umbel with multiple inflorescence primordia germinated in center,and floret primordia started to germinate in the young inflorescence.At T3,the inflorescence gradually became mature and many floret primordia germinated in the middle of inflorescence.At T4,floret primordia had developed into young floret inside the inflorescence.After Illumina sequencing,a total of 426,863,333 high quality paired-end clean reads were obtained.23621 and 26200 were identified as expressed in each cDNA library.What?s more,a total of 2838 DEGs were identified,of which 1495 DEGs were significantly down-regulated in P2 S and 1343 DEGs were significantly up-regulated.Compared to P2 S,217,470,1355 and 796 genes were identified to be differentially expressed in P2 M at T1,T2,T3 and T4 respectively.There are a large number of differentially expressed genes involved in protein processing in endoplasmic reticulum,plant hormone signal transduction and phenylpropanoid biosynthesis pathway.21 differentially expressed genes involved in plant hormone signal transduction and 22 DEGs involved in phenylpropanoid and flavonoids biosynthesis pathway were significantly down regulated in the CMS line at T3.In addition,12 mitochrondrial genes which participated in oxidative phosphorylation including ATP synthase,cytochrome c oxidase and NADH dehydrogenase genes exhibited low expression levels in P2 S at T3.The expression of 13 PPR related genes in P2 S was significantly lower than that in P2 M at T2,but 9 of them were significantly up-regulated in P2 S at T3 as compared to T2 and exceeded the expression level in P2 M.Similarly,the expression of 22 heat shock proteins which involved in the protein processing in endoplasmic reticulum pathway was significantly up-regulated in P2 S at T2-T3.Meanwhile,we also found that 9 MADS-box genes required for floral development were differentially expressed between P2 S and P2 M.The expression level of DcPI,DcAGL-1,DcAGL-2 and DcAGL-3 in P2 S was significantly lower than that in P2 M at T2,which may be the key reason leading to transformation from stamens into petal like structures.However,the expression of 9 MADS-box genes in P2 S suddenly increased from T2 to T3 and exceeded that in P2 M.This phenomenon was consistent with the expression pattern of PPR related gene and HSP genes at T3.