Different functional roles of RTR complex factors in DNA repair and meiosis in Arabidopsis and tomato

Abstract

The RTR (RecQ/Top3/Rmi1) complex has been elucidated as essential for ensuring genome stability in eukaryotes. Fundamental for the dissolution of Holliday junction (HJ)-like recombination intermediates, the factors have been shown to play further, partly distinct roles in DNA repair and homologous recombination. Across all kingdoms, disruption of this complex results in characteristic phenotypes including hyper-recombination and sensitivity to genotoxins. The type IA topoisomerase TOP3a has been shown as essential for viability in various animals. In contrast, in the model plant species Arabidopsis, the top3a mutant is viable. rmi1 mutants are deficient in the repair of DNA damage. Moreover, as opposed to other eukaryotes, TOP3a and RMI1 were found to be indispensable for proper meiotic progression, with mutants showing severe meiotic defects and sterility. We now established mutants of both TOP3a and RMI1 in tomato using CRISPR/Cas technology. Surprisingly, we found phenotypes that differed dramatically from those of Arabidopsis: the top3a mutants proved to be embryo-lethal, implying an essential role of the topoisomerase in tomato. In contrast, no defect in somatic DNA repair or meiosis was detectable for rmi1 mutants in tomato. This points to a differentiation of function of RTR complex partners between plant species. Our results indicate that there are relevant differences in the roles of basic factors involved in DNA repair and meiosis within dicotyledons, and thus should be taken as a note of caution when generalizing knowledge regarding basic biological processes obtained in the model plant Arabidopsis for the entire plant kingdom.

Crossover interference mechanism: New lessons from plants

“…Recq4 mutants increase by around three times the number of COs in rice, tomato, and pea (Mieulet et al, 2018). It seems that this RTR complex has functionally diverged between Arabidopsis and tomato (Whitbread et al, 2021).…”

Repair of DNA double-strand breaks in plant meiosis: role of eukaryotic RecA recombinases and their modulators

“…Certain point mutations in the Arabidopsis AtTOP3α and AtRMI1 also lead to an elevated level of meiotic CO frequency indicating that TOP3α-RMI1 possesses anti-crossover activity (Séguéla-Arnaud et al, 2015). The role of TOP3α-RMI1 has been studied in tomato and points to the differentiation of function of this complex between plant species (Whitbread et al, 2021).…”

Technology-driven approaches for meiosis research in tomato and wild relatives

“…Genome editing approaches have democratized reverse genetic studies in genetically transformable plant species, and this has facilitated an increase in the availability of meiotic mutants in a wide array of plant species (Wang et al 2021 ). Tomato is no exception—a number of studies have employed genome editing to generate DNA repair and meiotic mutants in tomato (Mieulet et al 2018 ; de Maagd et al 2020 ; Whitbread et al 2021 ). Through the detailed characterization of mutants in meiotic gene homologues in divergent plant species, and therefore different epistatic contexts, it will be possible to develop a more rounded view of meiotic gene function.…”

“…Specific Arabidopsis top3α (Séguéla-Arnaud et al 2015 ) and rmi1 (Séguéla-Arnaud et al 2017 ) mutants that lack C-terminal OB2 and Zinc Finger domains also exhibit increased meiotic CO, and are therefore separation-of-function mutants. In tomato null top3α mutants are embryo lethal, indicating a crucial role in early development, whereas predicted null rmi mutants do not have a highly disturbed meiosis and can produce pollen, fruits and seeds (Whitbread et al 2021 ). The different phenotypes of RTR complex mutants between Arabidopsis and tomato remain to be fully explained and highlight that further meiotic mutant generation in tomato will likely provide insights into the evolution of meiotic gene function.…”