Characterization Of The Expression Patterns Of Tomato SLGH3.2 And Its Potential Functions In Rice Plants

Auxin,one of the plant-produced hormones,has been well known to be a key signaling molecule that act in almost all physiological processes during plant growth and development,such as root system formation,organ development,vascular tissue formation and differentiation,systematic response to environmental stresses,and apical dominance,etc.The performance of normal function of auxin relies on its polar translocation and homeostasis in plants.The GH3 gene family is widely considered to be involved in a broad range of plant physiological processes,through modulation of hormonal homeostasis.Based on the phylogenetic relationships,plant GH3 genes have been classified into three major groups(?,? and ?).Multiple GH3 genes from Group II have been functionally studied and biochemically evidenced to have IAA-amido synthetase activity and confer auxin-inducible expression profiles.However,the function of GH3 genes from Group I and III have not been well studied,although several members from the two groups have been evidenced to show no response to external IAA application.Multiple GH3 genes have been functionally characterized in several model plant species,such as Arabidopsis and rice;however,to date,limited works to study the GH3 genes in tomato have been reported.In this study,though gnome-wide hunting of the released tomato genomic sequences,a total of 15 GH3 paralogues(SlGH3.1-15)have been identified from tomato,six of which(SlGH3.2,SIGH3.3,SIGH3.4,SIGH3.7,SIGH3.9 and SIGH3.15)could be divided into the Group II of GH3 family.Bioinformatics analysis revealed a relatively high conservation of gene sequence,exon/intron structure and chromosomal syntenies among these six paralogues.Phylogenetic analysis also revealed a very close relationships between SlGH3.2 and its orthologue AtGH3.1 from Arabidopsis.Detailed investigations,such as tissue-specific gene expression,and transcriptional regulatory profiles of the six tomato GH3 genes in response to external IAA applications and different nutrient(Pi and K)deficiency and high salt stress were also performed.In addition,the potential roles of SlGH3.2 were also characterized heterogenously in transgenic rice plants by its overexpression directed by a constitutive UBi promoter.The main results were as fellows:1.The tissue-specific expression patterns of the six tomato GH3 genes was determined in plants under normal growth condition.SlGH3.2 was shown to be mainly expressed in roots,flowers and mature fruits.No expression was detected for SlGH3.2 in stems and green fruits,while a very slight expression level could be detected in leaves.The expression of SlGH3.3 and SlGH3.4 were barely detected in almost all the tissues examined.With regard to the other three members,their expression could be detected to a certain extent in all the tissues.Within these six paralogues,SlGH3.2 was the member that had the highest expression level in roots?2.The expression patterns of the tomato GH3 genes in response to external IAA application was determined.All the six tomato GH3 genes from GH3 Group ? were found to show significantly inducible responses to external IAA.In particular,SlGH3.2 and SIGH3.4 were the two members that have more strong expression than the other four paralogues in the roots treated with external IAA.3.The expression patterns of the tomato GH3 genes in response to Pi-and K-deficiency as well as high salt stress was examined.It was shown that SlGH3.2 was significantly induced in the roots in response to Pi deficiency.The determination of the IAA and P concentration revealed that the total P concentrations in roots and leaves were both increased in the plants treated with external IAA application as compared to the untreated control plants,however,the IAA concentration in the roots was significant changed in the plant grown under Pi deficient condition.In addition,it was shown that both external IAA application and Pi deficient treatment could induce the lateral root development,which suggests a potential correlation between the induction of SlGH3.2 in response to low Pi supply condition and the Pi-starvation-mediated lateral root development.4.The IAA-and Pi-deficiency induced SlGH3.2 were introduced into transgenic rice using A.tumefaciens-mediated transformation.Overexpression of the SlGH3.2 in transgenic rice resulted in remarkably dwarfed phenotype and very less seeds with smaller size as compared to the wild-type plants.In addition,the expression levels of SlGH3.2 in different transgenic lines were observed to negatively correlative to the expression of two auxin-related expansin genes,Exp5 and Exp10,in rice.5.The determination of the IAA and P concentration in the transgenic and wide-type rice plants revealed that overexpression of SIGH3.2 in rice could significantly reduced the IAA concentration in roots and leaves;the total P concentration in the leaves of the transgenic rice were significant increased as compared to those in the wide-type rice plants,however,no significant changes of the P concentration in roots were observed between the wide type and transgenic rice plants.