Cloning And Effects Of TPS Family Members During Floral Bud Induction In �Nagafu NO.2' Apple Variety

Trehalose-6-phosphate(T6P)acts as an indicator of the sugar status in plants and functions as a crucial signaling molecule involved in the regulation of floral induction,and is closely related to sucrose.Trehalose-6-phosphate synthase(TPS)family members are pivotal components of the T6 P biosynthetic pathway.In this study,we identified apple TPS family members and investigated their expression patterns in different tissues.Additionally,�Nagafu No.2' apple trees were sprayed with sucrose and were de-fruited before the onset of floral induction.To study the effects of sucrose and de-fruit treatments on floral induction in apple trees and explore the physiological and molecular mechanisms of flowering,the expression of TPS genes responding to sucrose spraying and de-fruit treatments were analyzed,as well as in �Yangfu No.6'.The main results we obtained are as follows:1.Thirteen apple TPS family members were identified,and were grouped into two subfamilies based on their phylogenetic relationships and gene structures.Class I subfamilies consisted of three members(i.e.,MdTPS1,MdTPS2,MdTPS9).Class II contained ten members.Furthermore,there were more exons and introns in Class I TPS genes than in Class II genes.Besides,we cloned three Class I genes MdTPS1,MdTPS2,MdTPS9.The cDNA sequences of MdTPS1 and MdTPS2 were 75 nucleotides shorter than the corresponding genome sequences,while MdTPS9 was 114 nucleotides longer than expected.2.The expression patterns of the MdTPS genes differed in various tissues.MdTPS1 and MdTPS2 exhibited similar expression patterns,with the highest and lowest levels in stems and flowers,respectively.The highest and lowest MdTPS9 expression levels were observed in the flowers and buds,respectively.Additionally,the highest MdTPS3,4,6,7,and 11 expression levels were detected in fruits,while MdTPS5,12,and 13 were expressed most highly in flowers.The highest MdTPS8 and MdTPS10 expression levels were observed in buds.These results showed that MdTPS genes may participate in different organs development.3.Sucrose spraying and de-fruit treatments improved the sugar content in buds and increased bud size and fresh weight during floral inducton,as well as flowering rate.Addition-ally,thirteen apple TPS family members can respond to sucrose spraying and de-fruit treatments,as well as in different varieties.MdTPS1,2,4,and 11 had strong correlation with carbohydrate levels and floral induction.We speculated that MdTPS1,2,10,and 11 may respond to sucrose and regulate MdCO and MdSPL2 to activate downstream genes(i.e.,MdLFY,MdAP1)to induce flowering.4.We analyzed several motifs in the promoters of MdTPS genes.These motifs were associated with responses to phytohormones(i.e.,IAA,GA,ABA,JA,and SA)and light.It indicated MdTPS genes may control flowering by responding to phytohormones or light besides responding to sugar signal.