Characterization of GaWRKY1, a Cotton Transcription Factor That Regulates the Sesquiterpene Synthase Gene (+)-δ-Cadinene Synthase-A

Abstract

The cotton (+)-δ-cadinene synthase (CAD1), a sesquiterpene cyclase, catalyzes a branch-point step leading to biosynthesis of sesquiterpene phytoalexins, including gossypol. CAD1-A is a member of CAD1 gene family, and its promoter contains a W-box palindrome with two reversely oriented TGAC repeats, which are the proposed binding sites of WRKY transcription factors. We isolated several WRKY cDNAs from Gossypium arboreum. One of them, GaWRKY1, encodes a protein containing a single WRKY domain and a putative N-terminal Leu zipper. Similar to genes encoding enzymes of cotton sesquiterpene pathway, GaWRKY1 was down-regulated in a glandless cotton cultivar that contained much less gossypol. GaWRKY1 showed a temporal and spatial pattern of expression comparable to that of CAD1-A in various aerial organs examined, including sepal, stigma, anther, and developing seeds. In suspension cells, expression of both GaWRKY1 and CAD1-A genes and biosynthesis of sesquiterpene aldehydes were strongly induced by a fungal elicitor preparation and methyl jasmonate. GaWRKY1 interacted with the 3× W-box derived from CAD1-A promoter in yeast (Saccharomyces cerevisiae) one-hybrid system and in vitro. Furthermore, in transgenic Arabidopsis plants, overexpression of GaWRKY1 highly activated the CAD1-A promoter, and transient assay in tobacco (Nicotiana tabacum) leaves demonstrated that W-box was required for this activation. These results suggest that GaWRKY1 participates in regulation of sesquiterpene biosynthesis in cotton, and CAD1-A is a target gene of this transcription factor.

OsWRKY03, a rice transcriptional activator that functions in defense signaling pathway upstream of OsNPR1

“…receptor protein kinases and NPR1) [52,53]. Besides participating plant defense response, WRKY transcription factors also involve in the regulation of several other developmental and physiological processes such as trichome initiation [55], senescence [50], carbohydrate anabolism and secondary metabolism [56,57].…”

Gossypol: phytoalexin of cotton

“…Similarly, inoculation of bacteria on cotton cotyledons also induced the formation of cadinene-type sesquiterpenes (Davila-Huerta et al, 1995). Such inducement is faster in the resistant cotton cultivars of G. barbadense than in the susceptible cotton cultivars of G. hirsutum (Bianchini et al, 1999), and seems to be related to the jasmonate signaling, as jasmonate (MeJA) also induces gossypol accumulation and the gene expression (Luo et al, 2001;Xu et al, 2004). Consistently, expressions of biosynthesis pathway genes, including the HMGR, FPS, CDNs and as CYP706B1, have all been reported to exhibit inducible expression patterns upon stimulations (Joost et al, 1995;Liu et al, 1999a).…”

“…In Arabidopsis there are more than 70 WRKY family proteins (Dong et al, 2003), which share the conserved 60-amino acid WRKYGQK box and a zinc finger domain (Zhang et al, 2014). The G. arboreum WRKY protein GaWRKY1 shows temporal and spatial expression pattern comparable to that of CDN-A, and is able to bind to the W-box in promoter of CDN-A and activate its expression, suggesting its role in the regulation of sesquiterpenoid biosynthesis (Xu et al, 2004).…”

Indirect Defense Responses to Herbivory in Grasses

“…In Arabidopsis (Arabidopsis thaliana), a complex of jasmonic acid conjugate and COI protein targets a repressor of the JAZ family for degradation by the 26S proteasome and thereby activates genes of plant defense (Thines et al, 2007). Further transcription factors involved may be those of the WRKY family, which have already been implicated in the jasmonate-dependent expression of a terpene synthase in cotton (Gossypium hirsutum) responsible for the production volatile (+)-dcadinene (Xu et al, 2004). A recent review by Howe and Jander (2008) provides a comprehensive overview of the early signaling events after herbivory and the induction of the biosynthetic pathways involved in the production of plant volatiles.…”