Os01g0730700

WRKY14 is a candidate transcription factor for MeOH-induced Trp and serotonin biosynthesis.

Annotated Information

Function

Most WRKY proteins show a high binding affinity for the DNA sequence (T)(T)TGAC(C/T),also known as a W-box. During senescence of detached rice leaves, tryptophan (Trp) and Trp-derived secondary metabolites such as serotonin and 4-coumaroylserotonin accumulated in concert with methanol (MeOH) production. This senescence-induced MeOH induction was closely associated with levels of pectin methylesterase (PME)1 mRNA and PME enzyme activity. Exogenous challenge of detached rice leaves with 1% MeOH accelerated Trp and serotonin biosynthesis with induction of the corresponding genes.MeOH acts as an endogenous elicitor to enhance Trp biosynthesis.Approximately 800 genes were induced more than twofold in MeOH-treated leaves relative to those induced in water-treated leaves.All Trp biosynthetic genes were induced together with WRKY, Myb4, AP2/EREBP and ethylene-responsive tran-scription factors (ERTF), which have been implicated in plant biotic and abiotic responses.Only two WRKY genes,WRKY26 and WRKY14, from six WRKY transcription factors were suppressed significantly in the presence of cytokinin, and strikingly induced in the presence of ABA,suggesting that Trp and serotonin biosynthesis is mediated by WRKY tran-scription factors. Among many transcription factors induced following MeOH treatment, the WRKY family showed significant induction patterns, of which WRKY14 appeared to play a key regulatory role in MeOH-induced Trp and Trp-derived secondary metabolite biosynthesis. As shown in Pic3(d), WRKY14 bound to the TSa and TDC1 promoter W-box elements. Among several candidate W-box elements in the promoter sequences of TSa and TDC1, the strongest binding activity was observed for the TDC W5 sequence, which yielded two major DNA–protein complexes. In contrast, TSa W2 and TDC W1 revealed one major DNA–protein complex, whereas binding to theTSa W1 was negligible. The results suggest that WRKY14 interacts with the W-box elements of TS and TDC genes essential for Trp and serotonin biosynthesis. PME1 mRNA induction started at 12 h after senes-cence, followed by the induction of WRKY 26and WRKY14,suggesting that PME1-mediated MeOH production precedes the induction of WRKY mRNA.MeOH plays a role as an elicitor for inducing Trp and Trp-mediated secondary metabolite production via the WRKY14 transcription factors

Expression

Among the dozen genes tested, OsWRKY24, -51, -71, and -72 are induced by abscisic acid (ABA) in aleurone cells. Using a transient expression system, we have demonstrated that OsWRKY24 and -45 repress ABA induction of the HVA22 promoter-β-glucuronidase construct, while OsWRKY72 and -77 synergistically interact with ABA to activate this reporter construct. This study provides a solid base for functional genomics studies of this important superfamily of regulatory genes in monocotyledonous plants and reveals a novel function for WRKY genes, i.e. mediating plant responses to ABA.

Evolution

WRKY domains were initially defined by a nearly 60 amino acid long motif possessing the well-conserved amino acid signa-ture WRKYGQK at their N-terminus and containing a novel zinc finger-like structure of the form CX4–5CX22–23HXH.Variants of the WRKYGQK signa-ture motif include WRKYGKK and WRKYGEK. WRKY proteins containing a single WRKY domain are group II proteins; those with two are group I.Zhang and Wang (2005) have also proposed a different set of subgroups based on phylogenetic relationships.A third group, group III, contains a single WRKY domain with a variant zinc-finger CX7CX23HXC.Group IV WRKY proteins contain the WRKY motif, but lack a complete zinc-finger. There are a total of 102 copies of WRKY genes in indica rice; 99 are unique.In contrast, there are 98 copies of WRKY genes in japonica,97 are unique.Most pairs of indica and japonica orthologs are on corresponding chromosomes.Chromo-some 1 contains the highest number of WRKY genes. Overall, the densities of WRKY genes on each of the 12 chromosomes are similar in both subspecies. In fact, there are equal numbers of WRKY genes on six corresponding indica and japonica chromosomes (1, 2, 5, 6, 10, and 11). For the rest of the chromosomes, the numbers differ by only one or two.Clearly, WRKY genes are most abundant on chromosomes1 and 5. WRKY genes on chromosomes 1, 3, 5, 8, 11, and 12 are generally clustered together. A large duplication event between chromosomes 11 and 12 is apparent. A phylogenetic analysis of WRKY domains between rice and Arabidopsis shows WRKY domains of the same type forming independent domains within their species, suggesting that nu-merous WRKY gene duplications occurred after the divergence of the monocotyledons from dicotyledons some 50–80 million years ago.

Labs working on this gene

1.Department of Biotechnology, Interdisciplinary Program of Graduate School for Bioenergy and Biomaterials； 2.Bioenergy Research Center, Chonnam National University, Gwangju, 500-757, Republic of Korea； 3.Departme nt of Biol ogical Sci ences, Uni versity of N evada； 4.Bioinformatics Core, School of Life Sciences, University of Nevada

References

1.Kiyoon Kang, Sangkyu Park, Uyanga Natsagdorj, Young Soon Kim and Kyoungwhan Back.Methanol is an endogenous elicitor molecule for the synthesis of tryptophan and tryptophan-derived secondary metabolites upon senescence of detached rice leaves.The Plant Journal (2011) 66, 247–257 2.Zhen Xie,Zhong-Lin Zhang, Xiaolu Zou, Jie Huang,Paul Ruas, Daniel Thompson,and QingxiJ.Shen.Annotations and Functional Analyses of the Rice WRKY Gene Superfamily Reveal Positive a nd Negative Regulators of Abscisic Acid Signaling in Aleurone Cells.Plant Physiology(2005) Vol.137:176–189 3.Ross CA, Liu Y, Shen QJ.The WRKY gene family in rice (Oryza sativa).(2007)J. Integr. Plant Biol.49(6),827−842.