Sarah Melamed

The arms race between bacteria and phages led to the development of sophisticated antiphage defense systems, including CRISPR-Cas and restriction-modification systems. Evidence suggests that known and unknown defense systems are located in "defense islands" in microbial genomes. Here, we comprehensively characterized the bacterial defensive arsenal by examining gene families that are clustered next to known defense genes in prokaryotic genomes. Candidate defense systems were systematically engineered and validated in model bacteria for their antiphage activities. We report nine previously unknown antiphage systems and one antiplasmid system that are widespread in microbes and strongly protect against foreign invaders. These include systems that adopted components of the bacterial flagella and condensin complexes. Our data also suggest a common, ancient ancestry of innate immunity components shared between animals, plants, and bacteria.

The purpose of this study was to develop a model system for studying tomato genetics. Agronomic, genetic, and molecular data are presented which show that the miniature Lycopersicon esculentum cultivar, Micro‐Tom (Micro tomato), fulfills the requirements for such a model. It grows at high density (up to 1357 plants/m −2 ); it has a short life cycle (70–90 days from sowing to fruit ripening); and it can be transformed at frequencies of up to 80% through Agrobacterium ‐mediated transformation of cotyledons. Moreover, it differs from standard tomato cultivars by only two major genes. Therefore, any mutation or transgene can be conveniently studied in Micro‐Tom’s background and, when needed, transferred into a standard background. We took advantage of Micro‐Tom’s features to improve the infrastructure for mutagenesis in tomato. A screening of 9000 M1 and 20 000 M2 EMS mutagenized plants is described. Mutants with altered pigmentation or modified shape of leaves, flowers and fruits were found. In addition, an enhancer trapping and a gene trapping system, based on the Ac/Ds maize transposable elements, were transformed into Micro‐Tom and found to be active. In summary, Micro‐Tom opens new prospects to achieve saturated mutagenesis in tomato, and facilitates the application of transposon‐based technologies such as gene tagging, trapping and knockout.