The Polymorphism Display Of Transposon In Different Citrus Varieties

Bud mutation is one of the important variation sources of crop breeding such as citrus.Bud mutation is also an important type of somatic mutations in fruits.Many hybrids exist among citrus species.All kinds of hybrid citrus resources were derived from the interspecific hybridizations of basic citrus origins such as Citrus medica L,Citrus grandis(L.)Osbeck and Citrus reticulata Blanco.Bud mutation and hybridization events are the significant basis of citrus evolution and new varieties breeding.The molecular mechanism of bud mutation is unclear now.It is generally believed that the differences of bud mutation on molecular level are very tiny.To explore the transposon polymorphisms in different bud mutants,our aim was to find the markers which could identify the bud mutation varieties and it would advance the perspectives of the mechanism of bud mutation.In this way,it would contribute to provide a theoretical foundation of bud sport selection.Citrus had a highly hybrid genetic background.To study the activities of different transposons in the formation process of hybrid citrus,it conduced to understanding the genome varaiation of citrus hybrid materials and the evolution of species.Based on the citrus genome information,first of all,we used TD(transposon display)with thirty-three transposons to investigate the polymorphisms of different bud mutants.Then we selected twenty of all the transposons to observe the transposon polymorphisms in the hybrid citrus and their parents.The main results were as follows:1.We have selected thirty-three high abundance ratios of transposons to identify bud mutation.Five(DTM63,DTM58,Helitron1,Spem and m Ping2)of eighteen DNA transposons and four(Line1,LTR-Gypsy3,LTR-Gypsy5 and Tcs2)of fifteen retrotransposons could clearly identify the differences between bud mutants derived from the genetic variations including changes in fruit mature season,fruit color,seed fertility and so on.DTH3,an active DNA transposon,was highly polymorphic among sweet oranges,but was not obviously polymorphic in satsuma mandarin mutants.2.Some differences of transposons were detected between the Robertson navel orange and its early-maturing mutant Robertson35.As a result,Robertson navel orange and Robertson35 could be identified by DTM63,Spem and m Ping2.m Ping2 was an active transposon,and it could identify four pairs of bud mutants as following: Robertson navel orange and Robertson35,Anliu and Hong Anliu,the common ponkan and Qianyang seedless ponkan,red flesh and orange skin of Guanxi pummelo.3.As a kind of marker,transposons supported four types of hybridization events in different extent when sour orange(pummelo × mandarin),lemon(sour orange × citron),grapefruit(pummelo × sweet orange),clementina(mandarin × sweet orange)came into being.Ten of twenty transposons gave highest support to the hybrid sour orange from pummelo × mandarin.4.Three active transposons in the combination of pummelo,mandarin and sour orange were LTR-Copia1,Helitron1 and MUDR2;so as DTM53,DTM63 and MUDR2 were active in combination of pummelo,sweet orange and grapefruit.It was obvious that MUDR2 was active in the two different combinations.5.In the combination of pummelo,sweet orange and grapefruit,transposons had different performances.Some of Spem copies missed,Harbinger2 and LTR-Gypsy1 had no new activities,on the contrary,MUDR2 was active because it had new transpositions.