Wheat TaPUB1 Regulates Cd Uptake and Tolerance by Promoting the Degradation of TaIRT1 and TaIAA17

Abstract

Cadmium (Cd) accumulation in agricultural soils is an increasingly serious problem, as plants absorb Cd, which inhibits their growth and development. Nonetheless, the molecular mechanisms underlying Cd detoxification and accumulation in wheat (Triticum aestivum L.) are unclear. Here, we isolated the U-box E3 ligase TaPUB1 from wheat and reported the functional characterization of TaPUB1 in Cd uptake and tolerance in wheat. Under Cd stress, TaPUB1 overexpression lines displayed higher photosynthetic rates than the wild type; opposite results were observed in the TaPUB1-RNAi lines. In addition, TaPUB1 overexpression lines showed reduced Cd uptake and accumulation, whereas RNAi plants exhibited a significant increase in Cd accumulation after Cd treatment. We further found that TaPUB1 enhanced the resistance of wheat to Cd stress in three ways. First, TaPUB1 interacts with and ubiquitinates TaIRT1, resulting in the inhibition of Cd uptake. Second, TaPUB1 interacts directly with and ubiquitinates TaIAA17, facilitates its degradation, and results in primary root elongation by activating the Aux signaling pathway under Cd stress. Moreover, TaPUB1 decreases ROS accumulation by regulating antioxidant-related gene expression and antioxidant enzyme activity under Cd stress. Thus, a molecular mechanism by which TaPUB1 regulates Cd uptake and tolerance by modulating the stability of TaIRT1 and TaIAA17 proteins was revealed.

Plant E3 Ligases and Their Role in Abiotic Stress Response

“…Besides its role as a positive regulator of salt and drought stress in wheat [ 139 , 140 ], the PLANT U-BOX 1 (TaPUB1) was described as a positive regulator for Cd 2+ stress tolerance [ 141 ] ( Figure 7 ). Under Cd 2+ treatment (200μM CdCl 2 ), TaPUB1 overexpression lines exhibited a reduction in Cd 2+ accumulation in both roots and shoots and better survival rates and root growth in comparison to wildtype plants.…”

“…Under Cd 2+ treatment (200μM CdCl 2 ), TaPUB1 overexpression lines exhibited a reduction in Cd 2+ accumulation in both roots and shoots and better survival rates and root growth in comparison to wildtype plants. TaPUB1-RNAi lines showed opposite findings [ 141 ]. TaPUB1 interacts with IRON-REGULATED TRANSPORTER 1 (TaIRT1) and INDOLE-3-ACETIC ACID INDUCIBLE 17 (TaIAA17) and mediates their degradation via the 26S proteasome pathway [ 141 ].…”

“…TaPUB1-RNAi lines showed opposite findings [ 141 ]. TaPUB1 interacts with IRON-REGULATED TRANSPORTER 1 (TaIRT1) and INDOLE-3-ACETIC ACID INDUCIBLE 17 (TaIAA17) and mediates their degradation via the 26S proteasome pathway [ 141 ]. TaIRT1 is an iron transporter that facilitates Cd 2+ uptake.…”

“…TaIRT1 is an iron transporter that facilitates Cd 2+ uptake. Its accumulation in the root [ 217 , 218 ] suggests that TaPUB1-triggered degradation of TaIRT1 results in the observed reduced Cd 2+ accumulation [ 141 ]. TaIAA17 is a transcriptional regulator that functions as a repressor of auxin-inducible gene expression, and a negative regulator of root elongation growth [ 219 ].…”

“…Cd 2+ treatment reduced auxin levels in the plant, stabilized the suppression of auxin signaling by TaIAA17, and reduced root elongation [ 220 , 221 ]. This suggests that TaPUB1 counteracts Cd 2+ -dependent root growth by promoting TaIAA7 degradation [ 141 ].…”