Identification of WRKY Gene Family from Dimocarpus longan and Its Expression Analysis during Flower Induction and Abiotic Stress Responses

Abstract

Longan is an important fruit tree in the subtropical region of Southeast Asia and Australia. However, its blooming and its yield are susceptible to stresses such as droughts, high salinity, and high and low temperature. To date, the molecular mechanisms of abiotic stress tolerance and flower induction in longan have not been elucidated. WRKY transcription factors (TFs), which have been studied in various plant species, play important regulatory roles in plant growth, development, and responses to stresses. However, there is no report about WRKYs in longan. In this study, we identified 55 WRKY genes with the conserved WRKY domain and zinc finger motif in the longan genome. Based on the structural features of WRKY proteins and topology of the phylogenetic tree, the longan WRKY (DlWRKY) family was classified into three major groups (I–III) and five subgroups (IIa–IIe) in group II. Tissue expression analysis showed that 25 DlWRKYs were highly expressed in almost all organs, suggesting that these genes may be important for plant growth and organ development in longan. Comparative RNA-seq and qRT-PCR-based gene expression analysis revealed that 18 DlWRKY genes showed a specific expression during three stages of flower induction in “Sijimi” (“SJ”), which exhibited the “perpetual flowering” (PF) habit, indicating that these 18 DlWRKY genes may be involved in the flower induction and the genetic control of the perpetual flowering trait in longan. Furthermore, the RT-qPCR analysis illustrated the significant variation of 27, 18, 15, 17, 27, and 23 DlWRKY genes under SA (Salicylic acid), MeJA (Methyl Jasmonate), heat, cold, drought, or high salinity treatment, respectively, implicating that they might be stress- or hormone-responsive genes. In summary, we systematically and comprehensively analyzed the structure, evolution, and expression pattern of the DlWRKY genes. The results presented here increase our understanding of the WRKY family in fruit trees and provide a basis for the further elucidation of the biological function of DlWRKY genes in longan.

The WRKY Transcription Factor GmWRKY12 Confers Drought and Salt Tolerance in Soybean

“…According to classifications in the WRKY family [18,28,75], WRKY12 belongs to Group IIc and contains a single WRKY domain and a CX4-5CX22-23HXH zinc-finger motif. Recent studies have shown that the WRKYGQK heptapeptide, which can specifically recognize and bind to the W-box consensus sequence (TTGACY) in the promoters of target genes, can be replaced by WRKYGKK, WRKYGEK, WKKYEDK, or WKKYCEDK; variations of the WRKYGQK motif might change the DNA binding specificities to downstream target genes [75]. However, multiple sequence alignment results showed that WRKY12 in different species only harbor the same WRKYGQK heptapeptide, demonstrating that WRKY12 protein is evolutionarily conserved and can recognize and bind to downstream target genes (Figure 4A).…”

Genome-Wide Identification and Analysis of U-Box E3 Ubiquitin-Protein Ligase Gene Family in Banana

“…PUB proteins play important roles in regulating plant growth and development [34]. In the present study, the 29 MaU-box genes (MaU-box3/4/8/9/10/13/17/18/19/20/22/25/27/28/34/38/39/41/43/48/49/50/51/52/56/59/61/63/70) had the highest expression at the beginning of banana’s developmental stage (day 25), which could be explained by the fact that the highly expressed genes usually play important roles in plant development [35], suggesting ubiquitination activation through the first stages of fruit development. Of note, the expression of eight MaE2 genes [23] and three MaU-box genes decreased gradually with prolonged developmental time.…”

Transcriptome-wide identification and characterization of WD40 genes, as well as their tissue-specific expression profiles and responses to heat stress in Dimocarpus longan Lour.

“…By contrast, the D. longan roots and leaves are also used as traditional Chinese herbal medicine, but are not widely applied due to the little accumulation of flavonoids and other important secondary metabolites. Furthermore, the circumstance (e.g., high temperature) where the D. longan usually grows was another important factor adversely affecting their qualities and yields (Jue et al, 2018). Studies have shown that the biosynthesis of flavonoids, a complex biological process, is regulated by the WD40 TF family in plants (Liu et al, 2013).…”

“…Our previous studies suggested that the 4 bZIP genes that were differently expressed between D. longan roots and leaves might be involved in the secondary metabolite accumulations (Zheng et al, 2020). In D. longan, the up-regulated expressions of WRKY1, WRKY8, and WRKY50 correspondingly contributed to the tolerance to drought, heat, and cold stresses, respectively (Jue et al, 2018). Therefore, it is urgent to investigate the key TF which not only participate in flavonoid biosynthesis but also enhance abiotic resistances.…”