Molecular Identification of the G-Protein Genes and Their Expression Profiles in Response to Nitrogen Deprivation in Brassica napus

Heterotrimeric guanine nucleotide binding protein (G-protein) consisting of G alpha, G beta, and G gamma subunits is one of the key signal transducers in plants. Recent studies indicated that G-protein has been proposed as an important mediator of nitrogen responses in rice, wheat, and Arabidopsis. However, little is known about these G-proteins in Brassica napus (B. napus), except for three identified G-proteins, BnGA1, BnGB1, and BnGG2. Therefore, the aim of the present study is to characterize the members of the G-protein gene family in allotetraploid B. napus and to analyze their expression profiles in response to nitrogen deprivation. In total, 21 G-protein family members were identified in B. napus, encoding two G alpha, six G beta, and 13 G gamma. Sequence and phylogenetic analyses showed that although genome-wide triploid events increased the number of genes encoding G alpha, G beta, and G gamma subunits, the gene structure and protein properties of the genes encoding each G-protein subunit were extremely conserved. Collinearity analysis showed that most G-protein genes in B. napus had syntenic relationships with G-protein members of Arabidopsis, Brassica rape (B. rapa), and Brassica oleracea (B. oleracea). Expression profile analysis indicated that G alpha and C-type G gamma genes (except BnGG10 and BnGG12 were highly expressed in flower and ovule) were barely expressed in most organs, whereas most G beta and A-type G gamma genes tended to be highly expressed in most organs. G-protein genes also showed various expression patterns in response to nitrogen-deficient conditions. Under nitrogen deficiency, G alpha and five C-type G gamma genes were upregulated initially in roots, while in leaves, G alpha was downregulated initially and five C-type G gamma genes were highly expressed in different times. These results provide a complex genetic dissection of G-protein genes in B. napus, and insight into the biological functions of G-protein genes in response to nitrogen deficiency.

Automated summary

This study characterized the G-protein gene family in allotetraploid B. napus and analyzed their expression profiles in response to nitrogen deprivation. The results revealed the conservation of gene structure and protein properties among G alpha, G beta, and G gamma subunits. Collinearity analysis showed syntenic relationships between G-protein genes in B. napus and other Brassicaceae species. Expression profile analysis indicated organ-specific and nitrogen-responsive expression patterns of G-protein genes. These findings provide insight into the genetic dissection and biological functions of G-protein genes in B. napus.