Transcriptome-wide identification of bread wheat WRKY transcription factors in response to drought stress

Abstract

The WRKY superfamily of transcription factors was shown to be involved in biotic and abiotic stress responses in plants such as wheat (Triticum aestivum L.), one of the major crops largely cultivated and consumed all over the world. Drought is an important abiotic stress resulting in a considerable amount of loss in agronomical yield. Therefore, identification of drought responsive WRKY members in wheat has a profound significance. Here, a total of 160 TaWRKY proteins were characterized according to sequence similarity, motif varieties, and their phylogenetic relationships. The conserved sequences of the TaWRKYs were aligned and classified into three main groups and five subgroups. A novel motif in wheat, WRKYGQR, was identified. To putatively determine the drought responsive TaWRKY members, publicly available RNA-Seq data were analyzed for the first time in this study. Through in silico searches, 35 transcripts were detected having an identity to ten known TaWRKY genes. Furthermore, relative expression levels of TaWRKY16/TaWRKY16-A, TaWRKY17, TaWRKY19-C, TaWRKY24, TaWRKY59, TaWRKY61, and TaWRKY82 were measured in root and leaf tissues of drought-tolerant Sivas 111/33 and susceptible Atay 85 cultivars. All of the quantified TaWRKY transcripts were found to be up-regulated in root tissue of Sivas 111/33. Differential expression of TaWRKY16, TaWRKY24, TaWRKY59, TaWRKY61 and TaWRKY82 genes was discovered for the first time upon drought stress in wheat. These comprehensive analyses bestow a better understanding about the WRKY TFs in bread wheat under water deficit, and increased number of drought responsive WRKYs would contribute to the molecular breeding of tolerant wheat cultivars.

Novel Genomic and Evolutionary Insight of WRKY Transcription Factors in Plant Lineage

“…The WRKY TF gene family from various plant species, including A. thaliana 476, B. distachyon 14, G. raimondii 46, O. sativa 48, S. lycopersicum 51, T. aestivum 52 has been well elucidated. Surprisingly, when we combined the data from several published reports, none of them were found to be correlated with one another (Table 8).…”

“…Eulgem et al 4 has grouped WRKY TFs as groups I, IIa, IIb, IIc, IId, IIe, and III4 whereas, Wang et al 76 grouped them as IN, IC, IIa, IIb, IIc, IId, IIe and III76. Wu et al 48 grouped the WRKY TF gene family of O. sativa as Ia [NTWD (N-terminal WRKY domain), CTWD (C-terminal WRKY domain)], Ib, IIa, IIb, IIc, IId and III48, whereas Okay et al 52 grouped the WRKY TFs of T. aestivum as groups I, IIa, IIb, IIc, IId, IIe, and III52. Thus, there are hardly any consistencies in the grouping system of WRKY TFs.…”

“…Numerous studies have been conducted with WRKY TFs in different plant species, including Arabidopsis thaliana 4, Brachypodium distachyon 14, Gossypium raimondii 46, Lotus japonicas 47, Oryza sativa 48, Riccinus communis 49, Setaria italica 50, Solanum lycopersicum 51, Triticum aestivum 52, and Vitis vinifera 53. Different research groups have provided different grouping systems for the WRKY TFs, leading to lack of consistency in the grouping system.…”

The sunflower transcription factor HaWRKY76 confers drought and flood tolerance to Arabidopsis thaliana plants without yield penalty

“…Among plant TFs, those belonging to the WRKY family have been described as regulators of several developmental processes and related with biotic and abiotic stress responses in many plant species including the models Arabidopsis and rice, and also crops such as wheat, maize and sunflower (Chen et al 2015;Giacomelli et al 2010;Okay et al 2014;Raineri et al 2015;Rushton et al 2010Rushton et al , 2012. In particular, some WRKY transcription factors have been associated to the drought response, both as positive or as negative regulators (Ding et al 2014;Gong et al 2015;Sun and Yu 2015).…”

Gene expression analysis reveals important pathways for drought response in leaves and roots of a wheat cultivar adapted to rainfed cropping in the Cerrado biome

“…However, nowadays, the most preferred technique to evaluate gene expression is high-throughput cDNA sequencing (RNA-Seq) based on next-generation sequencing technology. Up till now, the use of RNA-seq, which is not limited to the number of transcripts pre-defined in probes, to study the drought response in bread wheat ( Triticum aestivum ) has been rare (Okay et al ., 2014; Liu et al ., 2015; Budak et al ., 2015). One obstacle to that type of study in bread wheat is the complexity of its hexaploid genome, which is estimated to be 17 gigabases in size and encoding more than 124,000 genes, of which approximately 76% of the assembled sequences contain repeats (IWGSC-International Wheat Genome Sequencing Consortium, 2014).…”