Abstract
Artemisia annua L. is well-known as the plant source of artemisinin, a sesquiterpene lactone with effective antimalarial activity. Here, a putative ortholog of the Arabidopsis thaliana WRKY40 transcription factor (TF) was isolated via reverse transcription-polymerase chain reaction and rapid amplification of cDNA ends in A. annua and named AaWRKY40. A putative nuclear localization domain was identified in silico and experimentally confirmed by using protoplasts of A. annua transiently transformed with AaWRKY40-GFP. A genome-wide analysis identified 122 WRKY genes in A. annua, and a manually curated database was obtained. The deduced proteins were categorized into the major WRKY groups, with group IIa containing eight WRKY members including AaWRKY40. Protein motifs, gene structure, and promoter regions of group IIa WRKY TFs of A. annua were characterized. The promoter region of AaWRKY group IIa genes contained several abiotic stress cis-acting regulatory elements, among which a highly conserved W-box motif was identified. Expression analysis of AaWRKY40 compared to AaWRKY1 in A. annua cell cultures treated with methyl jasmonate known to enhance artemisinin production, suggested a possible involvement of AaWRKY40 in terpenoid metabolism. Further investigation is necessary to study the role of AaWRKY40 and possible interactions with other TFs in A. annua.
Highlights
Most plant biosynthetic genes related to biotic and abiotic stress responses and/or involved in the production of secondary metabolites are under the control of different transcription factor (TF)families [1,2] and the cross-talk between the different members of each family amplifies the complexity of possible transcriptional regulatory roles [3].WRKY proteins are a large family of plant TFs involved in the regulation of several physiological processes including development, senescence, and immune response
Along with their role in regulating the expression of several genes, information on the role of WRKY TFs in activating pathways of plant secondary metabolites emerged including alkaloids, terpenoids, and phenylpropanoids [14,15] A CjWRKY1 was identified in Coptis japonica and transiently expressed in C. japonica protoplasts inducing an increased expression of genes involved in the biosynthesis of the alkaloid berberine [16]
We report on the isolation of a new WRKY (AaWRKY40) transcription factor in Artemisia annua homologous to the Arabidopsis group IIa AtWRKY18/40/60 genes and to GaWRKY1 of Gossypium arboreum
Summary
Most plant biosynthetic genes related to biotic and abiotic stress responses and/or involved in the production of secondary metabolites are under the control of different transcription factor (TF)families [1,2] and the cross-talk between the different members of each family amplifies the complexity of possible transcriptional regulatory roles [3].WRKY proteins are a large family of plant TFs involved in the regulation of several physiological processes including development, senescence, and immune response. Many reports have demonstrated that the transcription of WRKY genes is induced in plants after pathogen infection and, in turn, WRKY proteins may regulate the expression of several defense-related genes [9,13]. Along with their role in regulating the expression of several genes, information on the role of WRKY TFs in activating pathways of plant secondary metabolites emerged including alkaloids, terpenoids, and phenylpropanoids [14,15] A CjWRKY1 was identified in Coptis japonica and transiently expressed in C. japonica protoplasts inducing an increased expression of genes involved in the biosynthesis of the alkaloid berberine [16]. Xu et al [17] identified a cotton
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