[Cloning and expression of SmDXS2 gene in Swertia mussotii].

1-deoxy-D-xylulose-5-phosphate synthase2(DXS2) is the first key enzyme of the MEP pathway,which plays an important role in terpene biosynthesis of plants. According to the data of Swertia mussotii transcriptome, DXS2 gene(Gen Bank number MH535905) was cloned and named as Sm DXS2. The bioinformatics results showed that Sm DXS2 has no intron,with a 2 145 bp open reading frame encoding a polypeptide of 714 amino acids. They are belonging to 20 kinds of amino acids,and the most abundant amino acids include Ala,Gly and Trp. The predicted protein molecular weight was 76. 91 k Da and its theoretical isoelectric point(p I) was6. 5,which belonging to a hydrophilic protein. α-Helix and loop were the major motifs of predicted secondary structure of DXS2. The three function domains are TPP＿superfamily,Transket＿pyr＿ superfamily and Transketolase＿C superfamily,respectively. The Sm DXS2 protein shared high identity with other DXS2 proteins of plants. Phylogenetic analysis showed that Sm DXS2 protein is grouped with the gentian DXS2 protein. The recombinant protein of Sm DXS2 gene in Escherichia coli was approximately 92. 00 k Da(containing sumo-His tag protein 13 k Da),which was consistent with the anticipated size.This work will provide a foundation for further functional research of Sm DXS2 protein and increasing the product of iridoid compound by genetic engineering in S. mussotii.

Cotton S-adenosylmethionine decarboxylase-mediated spermine biosynthesis is required for salicylic acid- and leucine-correlated signaling in the defense response to Verticillium dahliae.

MAIN CONCLUSION: Cotton S-adenosylmethionine decarboxylase-, rather than spermine synthase-, mediated spermine biosynthesis is required for salicylic acid- and leucine-correlated signaling in the defense response to Verticillium dahliae. Spermine (Spm) signaling is correlated with plant resistance to the fungal pathogen Verticillium dahliae. We identified genes for key rate-limiting enzymes in the biosynthesis of Spm, namely S-adenosylmethionine decarboxylase (GhSAMDC) and Spm synthase (GhSPMS). These were found by screening suppression subtractive hybridization and cDNA libraries of cotton (Gossypium) species tolerant to Verticillium wilt. Both were induced early and strongly by inoculation with V. dahliae and application of plant hormones. Silencing of GhSPMS or GhSAMDC in cotton leaves led to a significant accumulation of upstream substrates and, ultimately, enhanced plant susceptibility to Verticillium infection. Exogenous supplementation of Spm to the silenced cotton plants improved resistance. When compared with the wild type (WT), constitutive expression of GhSAMDC in Arabidopsis thaliana was associated with greater Verticillium wilt resistance and higher accumulations of Spm, salicylic acid, and leucine during the infection period. By contrast, transgenic Arabidopsis plants that over-expressed GhSPMS were unexpectedly more susceptible than the WT to V. dahliae and they also had impaired levels of putrescine (Put) and salicylic acid (SA). The susceptibility exhibited in GhSPMS-overexpressing Arabidopsis plants was partially reversed by the exogenous supply of Put or SA. In addition, the responsiveness of those two transgenic Arabidopsis lines to V. dahliae was associated with an alteration in transcripts of genes involved in plant resistance to epidermal penetrations and amino acid signaling. Together, these results suggest that GhSAMDC-, rather than GhSPMS-, mediated spermine biosynthesis contributes to plant resistance against V. dahliae through SA- and leucine-correlated signaling.