Genome-wide analysis of the SAUR gene family and function exploration of DlSAUR32 during early longan somatic embryogenesis

The early auxin responsive small auxin up-regulated RNA (SAUR) family is an important gene family in the auxin signal transduction pathway. This study focused on the regulatory mechanism of DlSAUR genes during early somatic embryogenesis (SE) and its response to hormone treatment and abiotic stress. Mining of the available Dimocarpus longan Lour. (D. longan) genome sequence yielded 68 putative SAUR genes. Transcript profiles based on RNA-seq data showed that most of the 24 detected DlSAUR genes were highly expressed in the globular embryos (GE) (10) and most of them responded to heat stress and 2,4-D treatment. The results of qRT-PCR showed that most of DlSAUR genes were up-regulated under auxin inhibitor N-1-naphthylphthalamic acid (NPA) and auxin indole-3-acetic acid (IAA) treatments. Moreover, NPA could promote longan SE. The assay for ATAC-seq data analysis showed that chromatin accessibility of 19 of the 24 DlSAUR genes were open during early SE, and most DlSAUR genes differentially expressed during early SE were not associated with H3K4me1 signal enrichment. The DlSAUR32 was selected for subcellular localization and RNA-seq analysis, which encode a cell nuclear-localized protein. Dual-luciferase assays and transient transformation showed that the transcription factors (TFs) DlWRKY75-1 and DlWRKY75-2 might bind to the DlSAUR32 promoters to inhibition gene transcription. Transient overexpression of DlWRKY75-1 and DlWRKY75-2 decreased IAA content in N. benthamiana leaves. Thus, the regulatory network composed of DlSAUR32 and its related TFs may regulate the early longan SE and be involved in the auxin response regulatory pathway of longan.