| Peach(Prunus persica)gummosis is kind of damaging diseases in the south peach production area of Yangtze River Basin of China,which limits the healthy development of the peach promduction.One of the typical symptoms of peach gummosis is that the pathogen induces the formation and exudation large amounts of gum,which is mainly composed of heteropolysaccharides.Previous studies have shown that the transcripts of sugar metabolism and related gene are significantly changed in peach tissues after the peach gummosis fungus Lasiodiplodia theobromae(JMB-122)infection.SWEET(Sugars Will Eventually Be Exported Transporter)family is a novel class of sugar transporters that play important roles in seed germination,plant growth and development,and responding to abiotic/biotic stresses.When plants are infected with pathogens,SWEET genes are induced to be differentially expressed in plant defense response against pathogens.In this study,the expression profiles of SWEET members were analyzed in peach,as well as the function of PpSWEET2 b in the peach defense response against L.theobromae infection.The main results are as follows:1.The SWEET family has 20 members in peach.The expression levels of these SWEET genes were differentially expression in different tissues or organs at different growth and developmental stages in peach.q RT-PCR analysis showed that 10 genes were highly expressed in flowers and phloem,while 6 genes were highly expressed in fruits and leaves.Among them,PpSWEET7,PpSWEET9 b and PpSWEET2 a were highly expressed in the early to middle stage of flower(Fl S1 to Fl S3);and decreased at the late flower(Fl S5 to Fl S6).PpSWEET2 a,PpSWEET17 b and PpSWEET7 were up-regulated during the young fruit to fruit expanding period(Fr S1 to Fr S4),and decreased significantly in the late ripening stage of fruit(Fr S4 to Fr S5).The expression of PpSWEET10 was increased with fruit development and significantly higher in fruit mature period(Fr S5)than at other developmental periods.The expressions of PpSWEET2 b,PpSWEET17 a and PpSWEET17 b first increased and then decreased with leaf development and the expressions of PpSWEET1 a and PpSWEET15 increased significantly during leaf senescence.The expression of PpSWEET-like increased with branch age rising,whereas the expression of PpSWEET7,PpSWEET17 b,and PpSWEET2 a were higher in the phloem of one/two-year-old branches(SS1 to SS2)than those in the perennial branches(SS2 to SS5).In addition,two SWEET genes,PpSWEET1 b and PpSWEET5 a,were expressed below the detection level in flowers,fruits,stems,and leaves.2.A total of 6 SWEET family members were differentially expressed in the peach tissues infected by JMB-122,among which PpSWEET2 a,PpSWEET-like,PpSWEET17 a,PpSWEET17 b and PpSWEET7 were down-regulated,and PpSWEET2 b was differentially up-regulated.The expression of PpSWEET2 b was positively correlated with the pathogenicity of peach gummosis fungus after inoculation of peach shoots with different pathogenic strains(pathogenicity: JMB-122 > NP10 > LHKB-222 > XNHG-241 >LHKB-111).When different resistant varieties(susceptibility: ‘Spring snow’ > ‘Da hongpao’)were inoculated with JMB-122,the expression of PpSWEET2 b was significantly higher in ’Spring Snow’ than that in ‘Da hongpao’.The PpSWEET2b-silencing plants showed more resistance than control plant post inoculation with L.theobromae.The results demonstrated that PpSWEET2 b could play a negative role in peach against L.theobromae. |
