Integration of Transcriptome and Metabolome Provides Unique Insights to Pathways Associated with Wheat Immature Embryos Infected by Agrobacterium tumefaciens

Abstract

Background: The transformation efficiency (TE) of wheat is slow due to its recalcitrance nature to in vitro regeneration and genetic transformation. Nowadays, the TE of wheat immature embryo from cultivar Fielder in the PureWheat technique was greatly improved by a series of special chemical and physical methods. To explore the mechanisms of wheat high TE in this protocol, we strictly followed the procedures to obtain wheat immature embryos after Agrobacterium infection for 24 and 48 h, observed the surface of immature embryos using scanning electron microscope (SEM), and conducted comprehensive transcriptome and metabolome analysis. Results: SEM showed that Agrobacterium tumefaciens were deposited under the damaged cortex of wheat immature embryos caused by pretreatment and contacted the receptor cells to improve the TE. Transcriptome analysis showed that the differentially expressed genes were mainly enriched in phenylpropanoid biosynthesis, starch and sucrose metabolism, and plant-pathogen interaction, plant hormone signal transduction, MAPK signaling pathway. By analyzing the correlation between differentially expressed genes and metabolites, the expression of many genes and accumulation of metabolites are changed in glucose metabolism and the TCA cycle, as well as amino acid metabolism, it suggests that the wheat embryo infected with Agrobacterium is an energy demanding process. The shikimate pathway may act as a hub between glucose metabolism and phenylpropane metabolism during Agrobacterium infection. The down-regulation of F5H gene and up-regulation of CCR gene led to the accumulation of lignin precursor through phenylpropane metabolism. In addition, several metabolic pathways and oxidases were found to be involved in the infection treatment, including melatonin biosynthesis, benzoxazinoid biosynthesis, betaine biosynthesis, superoxide dismutase, peroxidase, which suggest that wheat embryo may be under the stress of Agrobacterium and thus undergo oxidative stress response. Conclusion: Our findings contribute to understand the underlying the mysterious mechanism of the high TE of wheat immature embryos stimulated by Agrobacteriumby exploring valuable genes and metabolites.