Poly-gamma-glutamic acid promoted maize root development by affecting auxin signaling pathway and the abundance and diversity of rhizosphere microbial community

Background: The root systems of higher plants play an important role in plant growth and development. In our present study, it was found that poly-gamma-glutamic acid (gamma-PGA), an environmentally friendly biomacromolecule, significantly improved root development in maize. Results: After treatment with gamma-PGA for 7 days, the fresh weight of maize roots was significantly increased and the differences between gamma-PGA treated group and control group were mainly caused by the number (higher by 71.87% compared to the control) and length of lateral roots. RNAseq and RT-PCR analyses showed that gamma-PGA treatment upregulated the expression of genes related to the synthesis of auxins and auxin signal in maize roots. In addition, gamma-PGA promoted the accumulation of plant growth-promoting bacteria, such as Azospirillum, Azohydromonas, Ramlibacter, and Sphingobium (Proteobacteria), Streptomyces (Actinobacteria), Parasegetibacter (Bacteroidetes), and Gemmatimonas (Gemmatimonadetes) in rhizosphere soil and the secretion of auxins. The results of this study deepened our understanding of the effects and mechanism of gamma-PGA on maize root development, and as well as highlighted the possibility of using gamma-PGA to improve crop growth and soil environment. Conclusions: gamma-PGA promotes early growth and development of maize roots by inducing the secretion and accumulation of auxin in roots and in rhizosphere soil, and increasing the abundance of plant growth promoting bacteria.