| Papaya(Carica papaya L.)is an economically important fruit crop in tropical and subtropical regions.Papaya is the 1st transgenic and the 5th angiosperm plant genome that has been fully sequenced.It has three different sex forms,female(XX),male(XY),and hermaphrodite(XYh).Sex determination in papaya is controlled by a XY sex chromosome system.Unlike the stable female flower in papaya,the phenotypes of male and hermaphrodite flowers can be changed by environmental factors.Under low temperature,male flower can change to hermaphrodite flower and produce fruit.Under stress conditions,hermaphrodite plants can produce infertile male flowers and malformed fruits,which subsequently reduces the yield.We sequenced transcriptomes of normal hermaphrodite flowers and pentandria flowers induced by high temperature,and performed differential gene expression as the first step to decipher the mechanism underlying the sex determination in papaya.We conducted differential gene expression analysis between the normal hermaphrodite flower(ZNHF)and pentandria hermaphrodite flowers(ZPHF),the normal hermaphrodite flower from EMS-treated trees(ETNHF)and pentandria hermaphrodite flowers from EMS-treated trees(ETPHF).Our differential gene expression analysis between ZNHF and ZPHF revealed 821 significantly differentially expressed genes.Gene ontology(GO)and Kyoto Encyclopedia of Genes and Genome(KEGG)pathway enrichment analysis showed that pollen development,and gametophyte development were enriched in up-regulated genes in biological process,and pollen tube development,and pollen tube growth were enriched in down-regulated genes.Circadian rhythm,and starch and sucrose metabolism were significantly enriched in up-regulated DGEs in ZPHF.Metabolism of xenobiotics by cytochrome P450 was enriched in downregulated DEGs in ZPHF.Among the 821 differentially expressed genes,there are 31 transcription factors and 86 hormone-related genes,most of which were related to the plant hormone signal transduction.There are 4 floral development-related gene.We also identified 23 differentially expressed genes from MSY,HSY and X counterpart regions.The expression of MYB24 was lower in ZPHF than in ZNHF.A total of 456 significantly differentially expressed genes were identified between ETNHF and ETPHF.GO analyze showed that oxidation-reduction,flavonoid biosynthesis,flavonoid metabolism,oxidoreductase activity,catalytic activity,and transferase activity were significantly enriched.KEGG analysis showed that plant hormone signal transduction was enriched.Among the 456 differentially expressed genes,there are 14 transcription factors and 33 hormone-related genes.Our results suggested that the pentandria flower induced by high temperature was likely caused by changing the expression of floral development genes,and plant hormone signal transduction and transcription factors played important roles in this process.Previous study showed difference of endogenous gibberellins in the three sex types of papaya.Other studies in maize,hemp and spinach also demonstrated that gibberellin can promote male formation.Therefore,we applied chlormequat chloride,a gibberellin suppressor,to papaya to study whether phytohormone can affect sex differentiation in papaya.We found 3 sex reversal plants in chlormequat chloride-treated plants.The length of the internodes decreased with the treatment of chlormequat chloride,which subsequently reduced the height of the plants.We collected leaves,flowers and apical meristems from control and chlormequat chloride-treatd plants,and performed differential gene expression analysis between control and treated samples.The results revealed the different responses to chlormequat treatment among leaves,flowers and apical meristems,and that the floral development was affected by chlormequat through regulating the expression of gibberellin biosynthesis-related genes and floral development-related genes. |
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