NBS1 promotes the endonuclease of the MRE11-RAD50 complex by sensing CtIP phosphorylation

DNA end resection initiates DNA break repair by homologous recombination. MRE11-RAD50-NBS1 and phosphorylated CtIP perform the first resection step by MRE11-catalyzed endonucleolytic DNA cleavage. Human NBS1, more than its Xrs2 homologue from Saccharomyces cerevisiae, is crucial for this process, highlighting complex mechanisms that regulate the MRE11 nuclease in high eukaryotes. Using a reconstituted system, we show here that NBS1, through its FHA and BRCT domains, functions as a sensor of CtIP phosphorylation. NBS1 then activates the MRE11-RAD50 nuclease through direct physical interactions with MRE11. In absence of NBS1, MRE11-RAD50 exhibits a weaker nuclease activity, which requires CtIP but not strictly its phosphorylation. This identifies at least two mechanisms by which CtIP promotes MRE11: a phosphorylation-dependent mode through NBS1, and a phosphorylation-independent mode without NBS1. In support, we show that limited DNA end resection in absence of the FHA and BRCT domains of NBS1 occurs in vivo. Collectively, our data suggest that NBS1 restricts the MRE11- RAD50 nuclease to S-G2 phase when CtIP is extensively phosphorylated. This defines mechanisms that regulate the MRE11 nuclease in DNA metabolism

Recent Advances in Breeding of Mango (Mangifera indica): A Review

Mango stands as a significant fruit crop with global importance, thriving primarily in tropical and subtropical regions across the world. (Mangifera indica L.) belongs to the Anacardiaceae family. This evergreen, sizable tree bears a beloved tropical fruit that enjoys local consumption and international trade. The choice of preferred mango varieties varies from one country to another. Generally, mango types from subcontinental Asian regions are monoembryonic, while those from South East Asian regions tend to be polyembryonic. Despite Mangifera indica's prevalence within the Mangifera genus, several other species within this genus share grafting and pollination compatibility with M. indica. These species can serve as valuable rootstocks or sources of novel genetic traits for breeders. Growing mango presents challenges due to the rapid decline in seed viability shortly after fruit maturity, typically within weeks. While a diverse array of mango varieties is available, inherent limitations exist, including extended juvenility, high clonal heterozygosity, the presence of only one seed per fruit, resilient seeds, polyembryony, early post-zygotic auto-incompatibility, and a substantial land requirement for hybrid evaluation. Breeders, however, benefit from the extensive variation and the ease of vegetative hybrid production. A successful mango cultivar must exhibit traits such as dwarfness, precocity, regular and prolific fruit bearing, appealing fruit of good size and quality, resistance to physiological issues, diseases, and insects, and an extended shelf life. A comprehensive understanding of mango phenology, inheritance patterns, and advanced techniques for hybridization has proven invaluable in addressing challenges like irregular fruit bearing, susceptibility to disorders and pests, and issues with taste and quality. The development of genetic markers has further reduced uncertainties in mango breeding and improved the management of hybrid populations

NBS1 promotes the endonuclease activity of the MRE11-RAD50 complex by sensing CtIP phosphorylation

DNA end resection initiates DNA double-strand break repair by homologous recombination. MRE11-RAD50-NBS1 and phosphorylated CtIP perform the first resection step via MRE11-catalyzed endonucleolytic DNA cleavage. Human NBS1, more than its homologue Xrs2 in Saccharomyces cerevisiae, is crucial for this process, highlighting complex mechanisms that regulate the MRE11 nuclease in higher eukaryotes. Using a reconstituted system, we show here that NBS1, through its FHA and BRCT domains, functions as a sensor of CtIP phosphorylation. NBS1 then activates the MRE11-RAD50 nuclease through direct physical interactions with MRE11. In the absence of NBS1, MRE11-RAD50 exhibits a weaker nuclease activity, which requires CtIP but not strictly its phosphorylation. This identifies at least two mechanisms by which CtIP augments MRE11: a phosphorylation-dependent mode through NBS1 and a phosphorylation-independent mode without NBS1. In support, we show that limited DNA end resection occurs in vivo in the absence of the FHA and BRCT domains of NBS1. Collectively, our data suggest that NBS1 restricts the MRE11-RAD50 nuclease to S-G2 phase when CtIP is extensively phosphorylated. This defines mechanisms that regulate the MRE11 nuclease in DNA metabolism

Treacle controls the nucleolar response to rDNA breaks via TOPBP1 recruitment and ATR activation

Induction of DNA double-strand breaks (DSBs) in ribosomal DNA (rDNA) repeats is associated with ATM-dependent repression of ribosomal RNA synthesis and large-scale reorganization of nucleolar architecture, but the signaling events that regulate these responses are largely elusive. Here we show that the nucleolar response to rDNA breaks is dependent on both ATM and ATR activity. We further demonstrate that ATM- and NBS1-dependent recruitment of TOPBP1 in the nucleoli is required for inhibition of ribosomal RNA synthesis and nucleolar segregation in response to rDNA breaks. Mechanistically, TOPBP1 recruitment is mediated by phosphorylation-dependent interactions between three of its BRCT domains and conserved phosphorylated Ser/Thr residues at the C-terminus of the nucleolar phosphoprotein Treacle. Our data thus reveal an important cooperation between TOPBP1 and Treacle in the signaling cascade that triggers transcriptional inhibition and nucleolar segregation in response to rDNA breaks