Abstract
Living organisms are constantly subject to DNA damage from environmental sources. Due to the sessile nature of plants, UV irradiation is a major genotoxic agent and imposes a significant threat on plant survival, genome stability and crop yield. In addition, other environmental chemicals can also influence the stability of the plant genome. Eukaryotic organisms have evolved a mechanism to cope with replication-blocking lesions and stabilize the genome. This mechanism is known as error-free DNA damage tolerance, and is mediated by K63-linked PCNA polyubiquitination. Genes related to K63-linked polyubiquitination have been isolated recently from model plants like Arabidopsis and rice, but we are unaware of such reports on the crop model Brachypodium distachyon. Here, we report the identification and functional characterization of two B. distachyon UBC13 genes. Both Ubc13s form heterodimers with Uevs from other species, which are capable of catalyzing K63 polyubiquitination in vitro. Both genes can functionally rescue the yeast ubc13 null mutant from killing by DNA-damaging agents. These results suggest that Ubc13-Uev-promoted K63-linked polyubiquitination is highly conserved in eukaryotes including B. distachyon. Consistent with recent findings that K63-linked polyubiquitination is involved in several developmental and stress-responsive pathways, the expression of BdUbc13s appears to be constitutive and is regulated by abnormal temperatures.
Highlights
Plants, due to their sessile nature, have developed unique and efficient mechanisms to cope with many environmental stresses including DNA damage
The in vivo results in this study revealed that both BdUBC13A and BdUBC13B could rescue the yeast ubc13 null mutant phenotypes to tolerate DNA-damaging agents and reduce spontaneous mutagenesis, characteristic of errorfree DNA-damage tolerance (DDT)
Since physical interactions of Ubc13 with yeast Mms2 and Rad5 are absolutely required for its error-free DDT activity in budding yeast (Xu et al, 2015), the above results indicate that BdUbc13 must be able to bind yeast Mms2 and Rad5 to form a functional E2–E3 complex
Summary
Due to their sessile nature, have developed unique and efficient mechanisms to cope with many environmental stresses including DNA damage. While sunlight is essential for photosynthesis, the resultant UV irradiation exerts strong influences on plant growth and development, and reduces crop yield by inducing DNA damage. High doses of UV irradiation exerts strong influences on plant growth and development, and reduces the crop yield by inducing DNA damage (Frohnmeyer and Staiger, 2003). In Saccharomyces cerevisiae, the PRR pathway is initiated by the stable E2–E3 complex Rad6–Rad. In Saccharomyces cerevisiae, the PRR pathway is initiated by the stable E2–E3 complex Rad6–Rad18 This pathway promotes replicative bypass of lesions encountered instead of removing them. The DDT pathway includes two branches, errorprone translesion synthesis (TLS) and error-free lesion bypass (Broomfield et al, 2001; Zhang et al, 2011) and they are achieved via sequential ubiquitination of proliferating cell nuclear antigen (PCNA). While PCNA monoubiquitination by Rad6– Rad promotes TLS, another E2–E3 complex, Mms2-Ubc13Rad, is thought to further ubiquitinate PCNA at the same K164 residue to form a K63-linked polyUb chain that is required for error-free lesion bypass (Hoege et al, 2002; Xu et al, 2015)
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