Background: Clerodendrum inerme (L.) Gaertn, a halophyte, usually grows on coastal beaches as an important mangrove plant. The salt-tolerant mechanisms and related genes of this species that respond to short-term salinity stress are unknown for us. The de novo transcriptome of C. inerme roots was analyzed using next-generation sequencing technology to identify genes involved in salt tolerance and to better understand the response mechanisms of C. inerme to salt stress. Results: Illumina RNA-sequencing was performed on root samples treated with 400 mM NaCl for 0 h, 6 h, 24 h, and 72 h to investigate changes in C. inerme in response to salt stress. The de novo assembly identified 98,968 unigenes. Among these unigenes, 46,085 unigenes were annotated in the NCBI non-redundant protein sequences (NR) database, 34,756 sequences in the Swiss-Prot database and 43,113 unigenes in the evolutionary genealogy of genes: Non-supervised Orthologous Groups (eggNOG) database. 52 Gene Ontology (GO) terms and 31 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were matched to those unigenes. Most differentially expressed genes (DEGs) related to the GO terms “single-organism process”, “membrane” and “catalytic activity” were significantly enriched while numerous DEGs related to the plant hormone signal transduction pathway were also significantly enriched. The detection of relative expression levels of 9 candidate DEGs by qRT-PCR were basically consistent with fold changes in RNA sequencing analysis, demonstrating that transcriptome data can accurately reflect the response of C. inerme roots to salt stress. Conclusions: This work revealed that the response of C. inerme roots to saline condition included significant alteration in response of the genes related to plant hormone signaling. Besides, our findings provide numerous salt-tolerant genes for further research to improve the salt tolerance of functional plants and will enhance research on salt-tolerant mechanisms of halophytes.

The primary constituents of the essential oil derived from Santalum album L. are (Z)-α-santalol, (Z)-β-santalol, (Z)-α-exo-bergamotol, and (Z)-epi-β- santalol. SaCYP736A167 plays a pivotal role in the biosynthesis of these sesquiterpene alcohols within S. album, but the mechanisms governing the expression of the SaCYP736A167 gene is far from being deciphered. In this research, a promoter sequence of the SaCYP736A167 gene, spanning 2808 base pairs, was isolated from S. album. A bioinformatics analysis of the 2384-bp SaCYP736A167 promoter (PSaCYP736A167) showed that abundant stress-inducible cis-acting elements were distributed in different regions of PSaCYP736A167. The histochemical β-glucuronidase (GUS) staining of T1 transgenic Nicotiana tabacum plants harboring PSaCYP736A167 demonstrated that the predominant GUS activity was exhibited in the parenchyma cells of the stem cortex and phloem, suggesting that PSaCYP736A167 is a tissue-specific expression promoter. GUS fluorometric assays of transiently transgenic N. benthamiana leaves revealed that seven distinct segments of PSaCYP736A167 exhibited notably varied levels of GUS activity. A 936-base pair sequence upstream of the transcription initiation codon ATG constitutes the core promoter section of PSaCYP736A167. Our findings shed light on the regulatory mechanisms controlling the transcription of the SaCYP736A167 gene, potentially serving as a novel tissue-specific promoter for applications in transgenic plant biotechnology.