The Mechanism Of Polyamines In Self-incompatibility In Pummelo

Citrus is the number one fruit in the world,and most of the resources represented by pummelo exhibit self-incompatibility.The self-incompatibility trait of pummelo is very likely to lead to low self-fruiting rate,and various pollination aids significantly increase the production cost.Polyamines play an important role in plant growth and development as well as stress tolerance,and it has been shown that exogenous polyamines can significantly increase self-fruit set in Rosaceae pears,but no effect has been reported in Rutaceae citrus.In the present study,we investigated the growth,physiological activity and gene expression of stigmas and pollen tubes in ‘Shatian’ pummelo using exogenous polyamines to determine whether polyamines were involved in the regulation of self-fertility in pummelo.The main results of the study are as follows:1.Spraying of exogenous 100 μM spermidine solution on self-pollinated styles significantly increased the length of self-pollen tubes in the style and significantly inhibited the expression of S-RNase genes in the style.Compared with cross-pollination,the polyamine content and the activities of catalase,superoxide dismutase and peroxidase significantly decreased and the level of reactive oxygen species significantly increased in the self-pollinated styles without polyamine treatment;however,the polyamine content and the activities of catalase,superoxide dismutase and peroxidase significantly increased and the level of reactive oxygen species significantly decreased in the self-pollinated styles after polyamine treatment.2.Expression of polyamine metabolism genes such as CgADC,CgSAMDC3 and CgPAO4 was significantly higher in style,anther and ovary tissues than in other tissues.Compared with cross-pollination,self-pollination resulted in significant up-regulation of the expression of the spermidine decarboxylase gene CgADC and the Sadenosylmethionine decarboxylase CgSAMDC1 gene,as well as the expression of the diamine oxidase genes CgDAO2 and CgDAO5 and the polyamine oxidase genes CgPAO4 and CgPAO5.Compared with ‘Shatian’ pummelo,the natural self-incompatibility mutation‘Gui’ pummelo significantly up-regulated the expression of CgADC and CgSPDS1 and CgSPDS2 of arginine decarboxylase gene,while CgDAO1,CgDAO2 and CgDAO5 of diamine oxidase gene were significantly down-regulated.dismutase gene CgSOD1 and peroxidase genes CgPOD1 and CgPOD2 were also significantly down-regulated.3.Self-S-RNase protein treatment inhibited the growth of isolated pollen tubes while significantly reducing the subserine content of pollen tubes,and significantly increased the expression of polyamine synthesis genes CgADC,CgSAMDC2 and CgSPMS2,and polyamine catabolism genes CgDAO5,CgPAO2 and CgPAO5 in pollen tubes.Inhibition of CgDAO5 gene expression increased spermine content and pollen tube length in self-SRNase protein-treated pollen tubes.50 μM spermine treatment significantly increased the length of isolated pollen tubes,but spermine above 200 μM significantly inhibited pollen tube growth.100 μM spermine significantly increased pollen tube length in self-S-RNase protein-treated pollen tubes and facilitated pollen tubes maintain their cytoskeletal structural integrity.Taken together,exogenous polyamine treatment can increase the polyamine content in living styles,reduce the level of reactive oxygen species,and inhibit the expression of S-RNase gene;it can also increase the length of isolated pollen tubes under self-S-RNase protein treatment.