Orthologs of the Class A4 Heat Shock Transcription Factor HsfA4a Confer Cadmium Tolerance in Wheat and Rice  

Abstract

Cadmium (Cd) is a widespread soil pollutant; thus, the underlying molecular controls of plant Cd tolerance are of substantial interest. A screen for wheat (Triticum aestivum) genes that confer Cd tolerance to a Cd hypersensitive yeast strain identified Heat shock transcription factor A4a (HsfA4a). Ta HsfA4a is most similar to the class A4 Hsfs from monocots. The most closely related rice (Oryza sativa) homolog, Os HsfA4a, conferred Cd tolerance in yeast, as did Ta HsfA4a, but the second most closely related rice homolog, Os HsfA4d, did not. Cd tolerance was enhanced in rice plants expressing Ta HsfA4a and decreased in rice plants with knocked-down expression of Os HsfA4a. An analysis of the functional domain using chimeric proteins constructed from Ta HsfA4a and Os HsfA4d revealed that the DNA binding domain (DBD) of HsfA4a is critical for Cd tolerance, and within the DBD, Ala-31 and Leu-42 are important for Cd tolerance. Moreover, Ta HsfA4a-mediated Cd resistance in yeast requires metallothionein (MT). In the roots of wheat and rice, Cd stress caused increases in HsfA4a expression, together the MT genes. Our findings thus suggest that HsfA4a of wheat and rice confers Cd tolerance by upregulating MT gene expression in planta.

Zinc-Finger Transcription Factor ZAT6 Positively Regulates Cadmium Tolerance through the Glutathione-Dependent Pathway in Arabidopsis

“…Several Arabidopsis transcription factors have been shown to be induced by heavy metal stress in plants; however, their physiological roles in heavy metal tolerance have not been clearly demonstrated (Herbette et al, 2006;Shim et al, 2009). A few transcriptional factors, such as CaPF1 and HsfA4a, were identified functioning in the Cd stress response (Tang et al, 2005;Shim et al, 2009). Overexpression of CaPF1, an ERF/AP2 pepper (Capsicum annuum) transcription factor, in transgenic VA pine (Pinus virginiana) confers tolerance to heavy metals Cd, Cu, and Zn, to heat, and to pathogens Bacillus thuringiensis and Staphylococcus epidermidis (Tang et al, 2005).…”

“…Plant responses to Cd stress involve the transcriptional regulation of numerous genes to establish an adaptive mechanism (Herbette et al, 2006;Weber et al, 2006;Shim et al, 2009). Several Arabidopsis transcription factors have been shown to be induced by heavy metal stress in plants; however, their physiological roles in heavy metal tolerance have not been clearly demonstrated (Herbette et al, 2006;Shim et al, 2009). A few transcriptional factors, such as CaPF1 and HsfA4a, were identified functioning in the Cd stress response (Tang et al, 2005;Shim et al, 2009).…”

“…These include ZNT1, OsHMA9, OsNRAMP5, ZntA, CAD2, AtPDR12, AtPDR8, AtATM3, ACBP1, Nramp5, EIN2, and MAN3 (Pence et al, 2000;Sharma et al, 2000;Shiraishi et al, 2000;Lee et al, 2003Lee et al, , 2007Kim et al, 2006Kim et al, , 2007Xiao et al, 2008;Cao et al, 2009;Lin and Aarts, 2012;Sasaki et al, 2012;Ishikawa et al, 2012;Chen et al, 2015). It was also found that Heat shock transcription factor A4a (HsfA4a) confers Cd tolerance by up-regulating MT gene expression in wheat (Triticum aestivum) and rice (Oryza sativa; Shim et al, 2009). Although these studies have unraveled some of the key players in Cd detoxification and tolerance in plants, the transcription factors that regulate the mechanisms of Cd detoxification have been poorly studied.…”

“…Cd has been demonstrated to inactivate or denature proteins by binding to sulfhydryl groups, which causes cellular damages by displacing cofactors from a variety of proteins, including transcription factors and enzymes (Goyer, 1997;Sharma et al, 2000;Schützendübel et al, 2001;Lin and Aarts, 2012). Moreover, Cd also induces oxidative stress, which in turn mediates cellular damage in various plants and animals (Shim et al, 2009;Gallego et al, 2012).…”

“…Cadmium (Cd) is one of the most dangerous environmental pollutants with high toxicity to animals and plants (Raskin et al, 1997;Lanphear, 1998;Kim et al, 2007;Shim et al, 2009;Lin and Aarts, 2012;Clemens et al, 2013;Dias et al, 2013). Cd has been demonstrated to inactivate or denature proteins by binding to sulfhydryl groups, which causes cellular damages by displacing cofactors from a variety of proteins, including transcription factors and enzymes (Goyer, 1997;Sharma et al, 2000;Schützendübel et al, 2001;Lin and Aarts, 2012).…”