Comparative transcriptome study of the elongating internode in elephant grass (Cenchrus purpureus) seedlings in response to exogenous gibberellin applications

Abstract

Bioenergy grass provides an important biomass resource for biofuel production worldwide. The internode elongation of grass stems is central to biomass production for biofuels; however, this process is poorly understood in elephant grass because it is a complex trait regulated by many genes. In this study, we adopted phenotypic, histological, transcriptomic, and phytohormone methods to investigate the regulatory mechanisms of internode elongation mediated by gibberellin (GA) in a dwarf cultivar and a standard cultivar. Phenotypic analysis revealed that exogenous GA3 increased plant height by inducing both internode length and internode number in two cultivars with contrasting internode lengths. Histological analysis revealed that the GA3 application increased the internode elongation through inducing both cell division and cell elongation. Phytohormone analysis indicated that exogenous GA3 treatment significantly increased endogenous indole-3-acetic acid (IAA), and zeatin (ZR) contents but decreased abscisic acid (ABA) contents, while the expression levels of genes related to hormone metabolism and signaling were substantially changed. Consistent with the expression pattern, a significant increase in lignin and cellulose content were also observed after GA3 treatment. Genes and transcription factors related to hormone metabolism and signaling, cell division, cell wall biosynthesis, and plant growth were identified as hub genes in the core coexpression network of the response to GA3 application. This study showed that active cell division, cell elongation, and cell wall biosynthesis contribute to internode elongation following exogenous GA3 applications and identified hub genes for these complex regulatory networks. These data elucidate mechanisms governing internode elongation in elephant grass and help breeders to develop elite cultivars with high biomass.