Genome-wide identification and expression analysis of the GAD family reveal their involved in embryogenesis and hormones responses in Dimocarpus longan Lour.

[Display omitted] • A total of 6 GAD family members were systematically identified in the whole genome of longan. DlGAD5 is localized in the cytoplasm. • DlGADs are involved in hormone synthesis and signaling for IAA and ABA in longan SE. • The expression of 6 DlGADs was up-regulated after overexpressing DlGAD5. Moreover, the activity of GAD was enhanced. Glutamate decarboxylase (GAD) is involved in GABA metabolism and plays an essential regulatory role in plant growth, abiotic stresses, and hormone response. This study investigated the expression mechanism of the GAD family during longan early somatic embryogenesis (SE) and identified 6 GAD genes based on the longan genome. Homology analysis indicated that DlGAD genes had a closer relationship with dicotyledonous plants. The analysis of cis -acting elements in the promoter region suggests that the GAD genes were associated with various stress responses and hormones. RNA sequencing (RNA-Seq) and the qRT-PCR data indicated that most DlGAD genes were highly expressed in the incomplete compact pro-embryogenic cultures (ICpEC) and upregulated in longan embryogenic callus (EC) after treatments with 2,4-D, high temperature (35 °C), IAA, and ABA. Moreover, the RNA-Seq analysis also revealed that DlGADs exhibit different expression patterns in various tissues and organs. The subcellular localization results showed that DlGAD5 was localized in the cytoplasm, suggesting that it played a role in the cytoplasm. Transient overexpression of DlGAD5 enhanced the expression levels of DlGADs and increased the activity of glutamate decarboxylase in longan embryogenic callus (EC), while the content of glutamic acid decreased. Thus, the DlGAD gene can play an important role in the early somatic embryogenesis of longan by responding to hormones such as IAA and ABA. DlGAD5 can affect the growth and development of longan by stimulating the expression of the DlGAD gene family, thereby increasing the GAD activity in the early SE of longan, participating in hormone synthesis and signaling pathways. [ABSTRACT FROM AUTHOR]