Members of BTB/TAZ family proteins are restricted to land plants. Arabidopsis genome encodes five members of this family, BT1-BT5 characterized by N-terminal BTB (bric-a-brac-/tramtrack/broad complex) domain, a transcriptional adapter zinc (TAZ) finger domain and a C-terminal calmodulin binding(CaMB) domain (Du and Poovaiah., 2004). Members of this family are divided into two groups, based on the presence of nuclear localization signals (NLSs) and leucine rich nuclear export signal (NESs) present in BT1 and BT2 but absent in BT3, BT4 and BT5. Based on the presence or absence of NLSs, they are either localized to both nucleus and cytoplasm or only cytoplasm. Their expression is induced by auxin treatment and based on BT mutants study, BT1, BT2 and BT3 play a redundant role in Arabidopsis gametophyte development (Robert et al., 2009). Sweetpotato BT-protein encoding gene lBT4 overexpression in Arabidopsis results in enhanced drought tolerance by upregulating BR signaling pathway and proline biosynthesis and by activating ROS scavenging system (Zhou et al., 2020). AtBT2 regulates telomerase activity in vegetative organs by acting as a target of TELOMERASE ACTIVATOR1 (TAC1). From in vivo yeast one hybrid assay and in vitro, TAC1 specifically binds to AtBT2 promoter and in response to TAC1 expression, AtBT2 AtBT2 mRNA levels increases whereas TAC1 mediated telomerase induction is blocked in AtBT2 null mutation (Ren et al., 2007). Recent study has shown that based on nuclear run on assays, mRNA decay studies and bisulfite sequencing, AtBT2 is required for maintaining transcriptional activation of multimerized Cauliflower mosaic virus 35S enhancer, in absence of which the 35S enhancer is silenced through hypermethylation. Based on CRISPR-cas9 editing of BT2, the TAZ domain and calmodulin binding domain is required for its 35S enhancer activity and function. To regulate the 35S enhancer activity, AtBT2 requires CULLIN3 and GTE9 (Global Transcription Factor group E proteins)and GTE11 proteins (Irigoyen et al., 2022)

Apple MdBT2 negatively regulates drought stress tolerance by binding to MdNAC143, a positive regulator of drought stress and ubiquitinating it and promoting its degradation via 26S proteasome system thus inhibiting MdNAC143 and several downstream genes involved in drought stress tolerance (Ji et al., 2020). In response to nitrate Malus domestica BT2 regulates malate accumulation and vacuolar acidification in apple, by directly binding to both MdCIbHLH1 and MdMYB73, ubiquitinating them and promoting 26S proteasome pathway mediated degradation of MdCIbHLH1 and MdMYB73. Since MdCIbHLH1 is a positive regulator of MdMYB73, their degradation  results in reduction of transcription of MdCIbHLH1 and MdMYB73 targeted genes like MdVHA-A, MdVHP1 and MdALMT9 involved in malate accumulation and vacuolar acidification (Zhang et al., 2020, Zhang et al., 2020). MdBT2 negatively regulates nitrogen-deficiency induced anthocyanin biosynthesis mediated by ABA, wounding, drought stress and high light (An et al., 2020) by promoting the degradation of MdMYB1, a key positive regulator of anthocyanin biosynthesis (Wang et al., 2018) and its interacting proteins such as MdbZIP44, MdWRKY40, MdERF38 and MdTCP46 that promotes anthocyanin biosynthesis (An et al., 2020). MdBT2 promotes nitrate induced plant growth in apple by binding directly to DELLA protein MdRGL3a, ubiquitinating it and degrading by 26S proteasome dependent pathway (Ren et al., 2021). There are 3, 7, 8, 9, 9, 9, 7, 14, 6, 10 and 6 TAZ genes in stiff brome, millet, sorghum, potato, pepper, maize, rice, apple, peach, pear, and tomato, respectively. Based on quantitative real-time PCR, the TAZ domain containing proteins are differentially expressed under various heavy metal stress conditions and promote resistance to metal stress mainly by interacting with OsMYB34 and OsFHA9 in rice (Shalmani et al., 2021). Arabidopsis BTB and TAZ domain protein BT4 positively regulates response to Botrytis cinerea wounding and inoculation by regulating the expression of genes involved in JA/ET signaling pathway. The BT4 T-DNA insertion mutant, bt4 after inoculation with B. cinerea, exhibited susceptibility as compared to wild type, complemented transgenic plants (CE) and overexpression transgenic plants (OE) (Zhou et al., 2022).

Last updated June 2023 by Ankita Abnave 

References:

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Zhou Y, Zhai H, He S, Zhu H, Gao S, Xing S, Wei Z, Zhao N, Liu Q. The Sweetpotato BTB-TAZ Protein Gene, IbBT4, Enhances Drought Tolerance in Transgenic Arabidopsis. Front Plant Sci. 2020 Jun 23;11:877. doi: 10.3389/fpls.2020.00877. PMID: 32655604; PMCID: PMC7324939.

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Zhang QY, Gu KD, Cheng L, Wang JH, Yu JQ, Wang XF, You CX, Hu DG, Hao YJ. BTB-TAZ Domain Protein MdBT2 Modulates Malate Accumulation and Vacuolar Acidification in Response to Nitrate. Plant Physiol. 2020 Jun;183(2):750-764. doi: 10.1104/pp.20.00208. Epub 2020 Apr 2. PMID: 32241879; PMCID: PMC7271804.

Zhang QY, Gu KD, Wang JH, Yu JQ, Wang XF, Zhang S, You CX, Hu DG, Hao YJ. BTB-BACK-TAZ domain protein MdBT2-mediated MdMYB73 ubiquitination negatively regulates malate accumulation and vacuolar acidification in apple. Hortic Res. 2020 Sep 2;7(1):151. doi: 10.1038/s41438-020-00384-z. PMID: 32944259; PMCID: PMC7468283.

Wang XF, An JP, Liu X, Su L, You CX, Hao YJ. The Nitrate-Responsive Protein MdBT2 Regulates Anthocyanin Biosynthesis by Interacting with the MdMYB1 Transcription Factor. Plant Physiol. 2018 Oct;178(2):890-906. doi: 10.1104/pp.18.00244. Epub 2018 Aug 28. PMID: 29807931; PMCID: PMC6181044.

An JP, Wang XF, Hao YJ. BTB/TAZ protein MdBT2 integrates multiple hormonal and environmental signals to regulate anthocyanin biosynthesis in apple. J Integr Plant Biol. 2020 Nov;62(11):1643-1646. doi: 10.1111/jipb.12940. Epub 2020 May 15. PMID: 32298027.

Ren YR, Zhao Q, Yang YY, Zhang R, Wang XF, Zhang TE, You CX, Huo HQ, Hao YJ. Interaction of BTB-TAZ protein MdBT2 and DELLA protein MdRGL3a regulates nitrate-mediated plant growth. Plant Physiol. 2021 May 27;186(1):750-766. doi: 10.1093/plphys/kiab065. PMID: 33764451; PMCID: PMC8154073.

Shalmani A, Ullah U, Muhammad I, Zhang D, Sharif R, Jia P, Saleem N, Gul N, Rakhmanova A, Tahir MM, Chen KM, An N. The TAZ domain-containing proteins play important role in the heavy metals stress biology in plants. Environ Res. 2021 Jun;197:111030. doi: 10.1016/j.envres.2021.111030. Epub 2021 Mar 24. PMID: 33774015.

Zhou F, Zhang K, Zheng X, Wang G, Cao H, Xing J, Dong J. BTB and TAZ domain protein BT4 positively regulates the resistance to Botrytis cinerea in Arabidopsis. Plant Signal Behav. 2022 Dec 31;17(1):2104003. doi: 10.1080/15592324.2022.2104003. PMID: 35876605; PMCID: PMC9318297.

Irigoyen S, Ramasamy M, Misra A, McKnight TD, Mandadi KK. A BTB-TAZ protein is required for gene activation by Cauliflower mosaic virus 35S multimerized enhancers. Plant Physiol. 2022 Jan 20;188(1):397-410. doi: 10.1093/plphys/kiab450. PMID: 34597402; PMCID: PMC8774732.