A grape VvHOS1-interacting HIPP protein (VvHIPP21) negatively regulates cold and drought stress

Heavy metal-associated isoprenylated plant proteins (HIPPs) are metallochaperones that contribute significantly to heavy metal homeostasis and detoxification processes. However, their specific regulatory roles in abiotic stresses are largely limited. Here, we show evidence that a HIPP21 from Vitis vinifera (named as VvHIPP21) is a novel functional component of the RING-type E3 ubiquitin ligase HOS1, which is recognized to be a key negative regulator of the cold signaling. VvHIPP21 gene is substantially suppressed in response to cold and ABA, but elevated by drought, and its product localized in both the cytoplasm and nucleus. Ectopic expression of 35 S:VvHIPP21 in Arabidopsis might alleviate the metal ion stress and the relative toxicity of Cu2+ and Cd2+, respectively. Notably, overexpression of VvHIPP21 alone or co-expression of VvHOS1 and VvHIPP21 greatly increase cold sensitivity in yeast, as evidenced by the survival rate of yeast cells under freezing stress conditions. Overexpression of VvHIPP21 in Arabidopsis resulted in cold sensitivity by down-regulating the cold-related genes of CBF-dependent pathway, relative to wild-type plants. In addition, VvHIPP21-overexpressing plants exhibited attenuated drought tolerance, as shown by an increased water loss rate, expanded stomatal aperture, accumulation of reactive oxygen species (ROS), and altered expression of ABA-dependent drought-responsive genes. Our results show that VvHIPP21 is favorably implicated in heavy metal homeostasis and detoxification, but adversely affects the cold signal pathway and ABA-mediated drought tolerance. Our findings shed light on how plants control growth and development in response to heavy metal and abiotic stresses.