Mechanisms Underlying The Formation Of Double Flower And Male Sterility Traits In Peach

Peach originated in China and has been cultivated for thousands of years in our country.Peach trees blossom first and then grow leaves,and the number of petals is the main ornamental character of peach flower.At present,the research on the peach flower mainly focuses on the flowering time and coloring mechanism,while the research on its double flower traits is less.Male sterility is an important agronomic trait for hybrid vigor utilization,but its underlying mechanisms remain to be uncovered.In this paper,we studied mechanisms underlying the formation of double flower and male sterility traits in the peach.The main results are as follows:Firstly,the regulation of ABCE model genes on double flower traits was studied.Nine ABCE model genes(PpAP1,PpAP2,PpAP3,PpPI,PpAG,PpSEP1,PpSEP2,PpSEP3,PpSEP4)were identified in the peach genome.PpAP2 belongs to the AP2 transcription factor family,and its gene structure contains 10 exons.The other eight genes belong to the MADS-box transcription factor family wth 7 or 8 exons.The results of subcellular localization showed that all 9 peach ABCE proteins were localized in the nucleus.We found that PpAP1,PpAP3,PpPI and PpSEP3 genes were not only differentially expressed in single flower and double flower peach varieties,but also highly expressed in petals and petaloid organs.The stamen of 35 S :: PpPI transgenic Arabidopsis lines had changed to petal and increased petal number;the number of rosette leaves in 35 S :: PpAP1 transgenic Arabidopsis lines decreased and promoted flowering;the 35 S :: PpAP3 and 35 S :: PpSEP3 transgenic Arabidopsis lines had no obvious floral phenotypic changed.The results of yeast two hybrid showed that there was interaction between peach ABCE proteins,and the effect of interaction on double flower traits needs to be further studied.These results indicate that the PpPI gene regulates the formation of the peach double flower.Secondly,the candidate genes located on Chr 2 for recessive peach double flower trait were identified.Thirteen candidate genes were identified by comparative transcriptome sequencing and whole genome sequencing.The expression level of these genes in peach double flower was lower than that in single flower,and they were mutated in the genome of the peach double flower.Finally,the cytology,physiology and potential genetic mechanism of the male sterility peach variety,‘Jinxiang' were analyzed.The dehiscence time of ‘Jinxiang'anthers was delayed and no pollen grains were released.Through the observation anthers section of ‘Jinxiang',it was found that the microspores in the mononuclear stage were severely vacuolated,then squeezed into strips,and finally degraded in anther cavity.The tapetal cells of ‘Jinxiang' swelled and proliferated with a lot of peroxisomes,and delayed degradation.The results of comparative transcriptome sequencing showed that genes in the reactive oxygen species scavenging pathways were differentially expressed in the peach male sterile variety ‘Jinxiang' and the normal fertile variety.And the content of glutathione-S-transferase,ascorbic acid peroxidase,glutathione,and carotenoid,which are mainly antioxidants of ‘Jinxiang' anthers decreased.These results indicated that the imbalance of reactive oxygen species homeostasis in ‘Jinxiang'anthers is closely related to the occurrence of male sterility.In addition,the cytological and physiological characteristics of the anthers of ‘Jinxiang' and the burst of reactive oxygen species in microspores development are similar to those of the rice ‘Honglian'-type cytoplasmic male sterile.And the expression of some genes in the mitochondria of ‘Jinxiang' were abnormal compared with normal fertility variety.It is speculated that the occurrence of male sterility in ‘Jinxiang' is determined by the mitochondrial genome variation.In conclusion,this study revealed the regulatory role of PpPI in the formation of double flower trait in peach,and identified candidate genes for recessive double flower trait,which laid a foundation for further analysis of the genetic mechanism of the peach double flower.In addition,the cytological,physiological,and potential genetic mechanisms of male sterility in ‘Jinxiang' peach were revealed,which provided theoretical support for the utilization of male sterility in peach.