Identification of AtHD2C as a novel regulator of ABA signaling in Arabidopsis thaliana

This report describes AtHD2C as a regulator of the ABA controlled events. AtHD2C is a member of the HD2-type histone deacetylase family. Results indicated an overall physiological significance for the HD2 proteins as well as a possible involvement in embryo development. In continuum with this, seeds overexpressing AtHD2C were insensitive to ABA, NaCl and mannitol at germination. This phenotype was supported by ABA-responsive gene expression patterns in the transgenic plants that implicated a negative role for AtHD2C in ABA response regulation in this developmental window. Additionally, the AtHD2C transcript accumulation was down-regulated by ABA that was reflected by the down-regulation of AtHD2C promoter driven GUS. In contrast to its function in the germination-post germination phase, AtHD2C seemed to play a positive role in ABA response regulation during the vegetative stage. AtHD2C overexpressing mature plants were able to survive extreme osmotic shock and drought conditions. The expression of AtHD2C promoter driven GUS in all vegetative tissues confirmed the presence of AtHD2C in this stage. The predominantly closed stomata and up-regulated ABA-responsive genes support the stress-tolerant phenotype of the 35S:AtHD2C transgenic plants. The information obtained from this investigation delineates a dual role for the AtHD2C in the regulation of the ABA response signaling in two developmental stages. (Abstract shortened by UMI.)

RTF2 controls replication repriming and ribonucleotide excision at the replisome

Abstract DNA replication through a challenging genomic landscape is coordinated by the replisome, which must adjust to local conditions to provide appropriate replication speed and respond to lesions that hinder its progression. We have previously shown that proteasome shuttle proteins, DNA Damage Inducible 1 and 2 (DDI1/2), regulate Replication Termination Factor 2 (RTF2) levels at stalled replisomes, allowing fork stabilization and restart. Here, we show that during unperturbed replication, RTF2 regulates replisome localization of RNase H2, a heterotrimeric enzyme that removes RNA from RNA-DNA heteroduplexes. RTF2, like RNase H2, is essential for mammalian development and maintains normal replication speed. However, persistent RTF2 and RNase H2 at stalled replication forks prevent efficient replication restart, which is dependent on PRIM1, the primase component of DNA polymerase α-primase. Our data show a fundamental need for RTF2-dependent regulation of replication-coupled ribonucleotide removal and reveal the existence of PRIM1-mediated direct replication restart in mammalian cells

Genomic signature of Fanconi anaemia DNA repair pathway deficiency in cancer

Fanconi anaemia (FA), a model syndrome of genome instability, is caused by a deficiency in DNA interstrand crosslink repair resulting in chromosome breakage1–3. The FA repair pathway protects against endogenous and exogenous carcinogenic aldehydes4–7. Individuals with FA are hundreds to thousands fold more likely to develop head and neck (HNSCC), oesophageal and anogenital squamous cell carcinomas8 (SCCs). Molecular studies of SCCs from individuals with FA (FA SCCs) are limited, and it is unclear how FA SCCs relate to sporadic HNSCCs primarily driven by tobacco and alcohol exposure or infection with human papillomavirus9 (HPV). Here, by sequencing genomes and exomes of FA SCCs, we demonstrate that the primary genomic signature of FA repair deficiency is the presence of high numbers of structural variants. Structural variants are enriched for small deletions, unbalanced translocations and fold-back inversions, and are often connected, thereby forming complex rearrangements. They arise in the context of TP53 loss, but not in the context of HPV infection, and lead to somatic copy-number alterations of HNSCC driver genes. We further show that FA pathway deficiency may lead to epithelial-to-mesenchymal transition and enhanced keratinocyte-intrinsic inflammatory signalling, which would contribute to the aggressive nature of FA SCCs. We propose that the genomic instability in sporadic HPV-negative HNSCC may arise as a result of the FA repair pathway being overwhelmed by DNA interstrand crosslink damage caused by alcohol and tobacco-derived aldehydes, making FA SCC a powerful model to study tumorigenesis resulting from DNA-crosslinking damage