DEAD-box (DDX) proteins belong to the largest subfamily of RNA helicase SF2, 
which contributes to all biological processes of RNA metabolism in the plant 
kingdom. Till now, no significant data are available regarding studies on DDX in 
Somatic Embryogenesis (SE) of woody plants. It is important to investigate the 
biological function of the DlDDX family in longan SE. Thus, a comprehensive 
analysis of 58 longan DEAD-box (DlDDX) genes characterization was performed by 
genome-wide identification and transcript abundance validation analysis. 
Homologous evolution has revealed that some DlDDXs in longan had high sequence 
similarity with Mus musculus, Citrus and Saccharomyces cerevisiae, indicating 
that DlDDXs were highly conservative in the animal, plant, and microorganism. 
Remarkably, gene duplication, purifying selection, and alternative splicing 
events, and new auxiliary domains have likely contributed to the functional 
evolution of DlDDX, indicating that DlDDX appeared neofunctionalization in 
longan. Besides, DlDDX3, 15, 28, 36 might interact with protein complex (MAC3A, 
MAC3B, CDC5, CBP20) of miRNA biosynthesis. Notably, DlDDX28 contained a novel 
auxiliary domain (CAF-1 p150), which might contribute to DNA demethylation in 
longan early SE. 4 DlDDX genes significantly expressed not only in early SE and 
zygotic embryogenesis (ZE) but also up-regulated at high levels in 'Honghezi' 
and 'Quanlongbaihe' with abortive seeds, which are of great significance. 
Moreover, some DlDDXs presented abiotic stress-response dynamic expression 
patterns by ABA, SA, JA, and NaCl treatments during early SE. Hence, DEAD-box is 
essential to SE development and seed abortive in longan.