Genome-wide analysis of the RGP gene family in Populus trichocarpa and their expression under nitrogen treatment.

Reversible glycosylation polypeptide (RGP) is a type of plant-specific protein, primarily involved in the biosynthesis of cell wall polysaccharides, which in turn changes the shape of the cell walls and affects the wood properties of plants. Poplar is a major industrial timber species, and the RGP gene has not been studied. This study uses bioinformatics methods to predict physical and chemical characters such as molecular weight, isoelectric point, and hydrophilicity; and fluorescent quantitative method to determine the effect of different forms of nitrogen on the transcription level of the gene family. The results showed that there are six RGP homologous genes in the Populus trichocarpa genome, which were distributed on the six chromosomes of P. trichocarpa. The family members have a simple gene structure and contain four exons and introns. Phylogenetic tree analysis showed that RGP genes all belong to Class I in P. trichocarpa. Tissue-specific expression analysis showed that PtRGP1 and PtRGP2 were highly expressed in the stems, PtRGP4 and PtRGP5 were highly expressed in the upper leaves, PtRGR3 and PtRGR6 were expressed in stems and internodes, but the relative expression is not high. Quantitative real-time RT-PCR (qRT-PCR) analyses revealed that PtRGP3 and 6 were up-regulated in the upper stem in response to the low ammonium and high nitrate treatments. The influence of nitrogen on the expression of PtRGP3 and 6 genes may affect the formation of the plant secondary cell wall. This study lays a foundation for further study on the function of RGP genes in P. trichocarpa.