Spatio-temporal expression profiles and functional suppression of wheat defense responses by a salivary protein gene,Sg1655,from the spring-grain aphid Schizaphis graminum
To further elucidate the role of the functionally unknown salivary protein Sg1655 in regulat-ing the defense response of wheat,this study was carried out based on transcriptomic data from the sali-vary glands of Schizaphis graminum.The open reading frame of Sg1655 was obtained via PCR,and se-quence analysis was performed using bioinformatics software.The expression level of Sg1655 in differ-ent aphid tissues and instars was measured using real-time quantitative PCR(RT-qPCR).Sg1655 was delivered into wheat leaves using a bacterial type Ⅲ secretion system to examine the effect of its tran-sient expression on callose accumulation in wheat.The results showed that the full-length open reading frame of Sg1655 was 375 bp,encoding 125 amino acid residues,with the N-terminal 1-21 sequence representing the signal peptide.The predicted protein molecular weight was 14.90 kD.Multiple se-quence alignment revealed that the ammo acid sequence of Sg1655 from S.graminum shared the high-est sequence identity(89.52％)with the homologous sequence of Rhopalosiphum maidis.Sg1655 clus-tered into one branch with the homologous sequences of R.maidis,indicating a close genetic relation-ship between them.Sg1655 was found to be expressed in all aphid tissues,with the highest expression level in the salivary gland.In addition,Sg1655 expression was detected in all instars of S.graminum,with no significant difference in expression levels among various instars.Transient expression of Sg1655 significantly suppressed the accumulation of callose in wheat,indicating that the salivary pro-tein Sg1655 may be involved in suppressing wheat defense responses as a potential effector.
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