Objective   Belonging to the 15^th subgroup of basic helix-loop-helix (bHLH) transcription factor family that associated with the growth, development, and stress resistance of plants, PIF family of Dimocarpus longan Lour were identified and their expressions studied.

  Method   PIFs were identified, and bioinformatics extracted from the longan genome and transcriptome database. Cis-acting elements were analyzed for the promoter sequence. Expressions of DlPIFs during early SE (i.e., embryogenic callus or EC, incomplete embryotic compacted structure or ICpEC, and spherical embryo or GE), in different tissues (including flower, flower bud, leaf, pericarp, pulp, root, seed, stem, and young fruit), under different light (e.g., blue, bright, and dark), and at varied temperatures (i.e., 15℃, 25℃, and 35℃) were obtained from the FPKM values. In addition, expressions of the genes in early SE exposed to exogenous hormones such as 2,4-D, ABA, GA3, SA, MeJA were determined by qRT-PCR.

  Result   All DlPIFs had the bHLH domain. The lengths of their coding region ranged from 975 bp to 2298 bp each consisted of 5–8 exons, 4–7 introns, and 6 motifs. The DlPIFs were in the nucleus with promoters containing not only the acting elements in response to light, hormone, and abiotic stress but also those to seed growth and embryonic development. The phylogenetic tree of DlPIFs distributed in 4 branches closely related to Arabidopsis thaliana and Citrus sinensis (L.) Osbeck. The transcriptomes of different tissues and organs showed the highest expression of DlPIF1-1 in the seeds, that of DlPIF1-2 in the pulp, that of DlPIF4 in the stems, that of DlPIF5 in the flower buds, and those of DlPIF7 and DlPIF8 in the leaves. The photometric transcriptomes indicated that the expressions of DlPIF1-1, DlPIF5, and DlPIF8 under blue light were significantly higher than that of control, that of DlPIF4 under white or blue light significantly higher than that of control, and that of DlPIF1-2 did not differ significantly under different light exposures. At 35^oC, the relatively high temperature heightened the expressions of DlPIF4 and DlPIF6 but depressed those of DlPIF1-1, DlPIF1-2, DlPIF3, and DlPIF8. At 15 ℃, on the other hand, the expressions of DlPIF1-1, DlPIF3, and DlPIF5 were enhanced, while those of DlPIF1-2, DlPIF4, DlPIF6, and DlPIF8 inhibited. qRT-PCR results showed that the expressions of DlPIF1-1, DlPIF5, DlPIF6, and DlPIF8 decreased with the longan embryonic development at the early stage. Those of DlPIF1-2, and DlPIF3 decreased from EC to ICpEC, those of DlPIF4 and DlPIF7 decreased from ICpEC to GE, and those of DlPIF4 and DlPIF7 were the opposite. In response to the exposure to 5 exogenous hormones, DlPIF5 and DlPIF7 expressed significantly different from the others.

  Conclusion   DlPIFs might have varied functions associated with the growth and development, as well as biological and/or abiotic stress responses, of longan.