Objective GRAS transcription factors play an important regulatory role in plant defense response, root development, meristem formation, gibberellin (GA) signaling and optical signal transduction. Members of the GRAS gene family in paper mulberry were identified and their expression patterns in stem tissues were analyzed, which could provide a reference for studying the lignification and development of paper mulberry stems.

Method HMM was used to identify GRAS family genes in the whole genome of paper mulberry, and the expression patterns of GRAS genes in paper mulberry stem tissues (T1-T3) with different lignification degrees were analyzed through bioinformatics methods and RNA-Seq data.

Result A total of 43 members of the GRAS family from the genome of paper mulberry was identified, and they were named according to their chromosome distribution.74% of BpGRAS had no introns, and 23% of BpGRAS contained only 1 to 2 introns. Most BpGRAS proteins were acidic amino acids, unstable proteins, and hydrophilic proteins. The secondary structure was dominated by irregular curls and alpha helices. Phylogenetic and protein conserved structure analysis were carried out together with Arabidopsis GRAS protein. The results showed that the 43 GRAS members of paper mulberry were divided into 9 categories and had high homology with Arabidopsis GRAS protein. The analysis of cis-acting elements showed that this family may have potential functions in the related biological processes of plant photoreaction, response to adversity stress, and regulation of plant-derived hormones. Expression analysis based on RNA-Seq showed that BpGRAS6 and BpGRAS11 were continuously significantly up-regulated in T1-T3, and BpGRAS1, BpGRAS15, BpGRAS20, BpGRAS23, and BpGRAS29 were continuously significantly down-regulated in T1-T3.

Conclusion In this study, 43 members of the GRAS gene family were identified from the genome of paper mulberry. It was hypothesized that BpGRAS6, BpGRAS11, BpGRAS1, BpGRAS15, BpGRAS20, BpGRAS23, and BpGRAS29 may play a role in the formation of the xylem of paper mulberry stems. They can be used as candidate genes to study the regulatory mechanism of paper mulberry lignification.