ArabidopsisPUB22 and PUB23 Are Homologous U-Box E3 Ubiquitin Ligases That Play Combinatory Roles in Response to Drought Stress

Abstract

Ubiquitination is involved in diverse cellular processes in higher plants. In this report, we describe Arabidopsis thaliana PUB22 and PUB23, two homologous U-box-containing E3 ubiquitin (Ub) ligases. The PUB22 and PUB23 genes were rapidly and coordinately induced by abiotic stresses but not by abscisic acid. PUB22-and PUB23-overexpressing transgenic plants were hypersensitive to drought stress. By contrast, loss-of-function pub22 and pub23 mutant plants were significantly more drought-tolerant, and a pub22 pub23 double mutant displayed even greater drought tolerance. These results indicate that PUB22 and PUB23 function as negative regulators in the water stress response. Yeast two-hybrid, in vitro pull-down, and in vivo coimmunoprecipitation experiments revealed that PUB22 and PUB23 physically interacted with RPN12a, a subunit of the 19S regulatory particle (RP) in the 26S proteasome. Bacterially expressed RPN12a was effectively ubiquitinated in a PUB-dependent fashion. RPN12a was highly ubiquitinated in 35S:PUB22 plants, but not in pub22 pub23 double mutant plants, consistent with RPN12a being a substrate of PUB22 and PUB23 in vivo. In water-stressed wild-type and PUBoverexpressing plants, a significant amount of RPN12a was dissociated from the 19S RP and appeared to be associated with small-molecular-mass protein complexes in cytosolic fractions, where PUB22 and PUB23 are localized. Overall, our results suggest that PUB22 and PUB23 coordinately control a drought signaling pathway by ubiquitinating cytosolic RPN12a in Arabidopsis.

Proteasome regulation, plant growth and stress tolerance

“…25 Indeed, AtPUB22/23 overexpression caused hypersensitivity to drought stress, while their loss of function resulted in drought tolerance. 21,22 This is somewhat paradoxical since the stress-induced expression of both ligases suggested that they are needed by plant cells to counteract the negative impact of the stress. The AtPUB22/23 overexpression studies did reveal two potentially beneficial traits for plants subjected to water stress: increased root elongation, which increases a plants' ability to maintain water uptake, and accelerated flowering that secures the production of progeny under adverse conditions.…”

“…[21][22][23] The hot pepper (Capsicum annuum L.) U-box protein 1 (CaPUB1) and its Arabidopsis homologues AtPUB22 and AtPUB23 are Ub ligases, and the corresponding genes are rapidly induced by abiotic stresses such as desiccation, cold and mechanical wounding. 21,22 Both the hot pepper and Arabidopsis PUBs seem to interfere with 26SP function by ubiquitinating specific subunits of the RP lid subcomplex. CaPUB1 ubiquitinates RPN6, and because the RPN6 level was reduced in CaPUB1 overexpressing plants, it has been suggested that the ubiquitination leads to the destabilization of this RP subunit.…”

The E3 Ligase TaSAP5 Alters Drought Stress Responses by Promoting the Degradation of DRIP Proteins

“…For example, in Arabidopsis (Arabidopsis thaliana), the 26S proteasome-mediated degradation of DEHYDRATION-RESPONSIVE ELEMENT BINDING PROTEIN2A (DREB2A) is promoted by the negative regulators of drought-responsive gene expression DREB2A-INTERACTING PROTEIN1 (DRIP1) and DRIP2 (Qin et al, 2008). The Arabidopsis U-box-type E3 ubiquitin ligases PLANT U-BOX22 (PUB22) and PUB23 jointly regulate a drought signaling pathway by ubiquitinating cytosolic REGULATORY PARTICLE NON-ATPASE12A (Cho et al, 2008) and drought stress-induced Rma1H1, which is a hot pepper (Capsicum annuum) homolog of a human RING (Really Interesting New Gene) membraneanchor1 E3 ubiquitin ligase that regulates aquaporin levels via ubiquitination (Lee et al, 2009a). Triticum durum RING Finger1 (TdRF1) may act as a nuclear E3 ligase in durum wheat, where it regulates the abiotic stress response by promoting degradation of the WHEAT BEL1-TYPE HOMEODOMAIN1 (WBLH1) transcription factor through the 26S proteasome in vivo (Guerra et al, 2012).…”

Bacterial effector modulation of host E3 ligase activity suppresses PAMP-triggered immunity in rice

“…Arabidopsis AtPUB22, AtPUB23 and AtPUB24 redundantly and negatively regulate PTI 10 . In addition, AtPUB22 and AtPUB23 also function as negative regulators in the water-stress response 36 . Recently, Exo70B2, a component of the exocytic machinery, was identified as a substrate for AtPUB22 (ref.…”