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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.

Floral reversion is a process in which differentiated floral organs revert back to vegetative organs. Although this phenomenon has been described for decades, the underlying molecular mechanisms remain unclear. In this study, we found that immature switchgrass (Panicum virgatum) inflorescences can revert to neonatal shoots when incubated on a basal medium with benzylaminopurine. We used anatomical and histological methods to verify that these shoots were formed from floret primordia through flower reversion. To further explore the gene regulation of floral reversion in switchgrass, the transcriptome of reversed, unreversed, and uncultured immature inflorescences were analyzed and 517 genes were identified as participating in flower reversion. Annotation using non-redundant databases revealed that these genes are involved in plant hormone biosynthesis and signal transduction, starch and sucrose metabolism, DNA replication and modification, and other processes crucial for switchgrass flower reversion. When four of the genes were overexpressed in Arabidopsis thaliana, vegetative growth was facilitated and reproductive growth was inhibited in transgenic plants. This study provides a basic understanding of genes regulating the floral transition in switchgrass and will promote the research of floral reversion and flower maintenance.