A memory switch for plant synthetic biology based on the phage ϕC31 integration system

Synthetic biology has advanced from the setup of basic genetic devices to the design of increasingly complex gene circuits to provide organisms with new functions. While many bacterial, fungal and mammalian unicellular chassis have been extensively engineered, this progress has been delayed in plants due to the lack of reliable DNA parts and devices that enable precise control over these new synthetic functions. In particular, memory switches based on DNA site-specific recombination have been the tool of choice to build long-term and stable synthetic memory in other organisms, because they enable a shift between two alternative states registering the information at the DNA level. Here we report a memory switch for whole plants based on the bacteriophage ϕC31 site-specific integrase. The switch was built as a modular device made of standard DNA parts, designed to control the transcriptional state (on or off) of two genes of interest by alternative inversion of a central DNA regulatory element. The state of the switch can be externally operated by action of the ϕC31 integrase (Int), and its recombination directionality factor (RDF). The kinetics, memory, and reversibility of the switch were extensively characterized in Nicotiana benthamiana plants.

Optimization of transconjugation and characterization of attB integration site for Streptomyces cinnamoneus producing transglutaminase

An effective transformation method for molecular genetic studies of Streptomyces cinnamoneus producing transglutaminase was established using intergeneric conjugal transfer based on the bacteriophage ϕC31 att/int system. The high efficiency of S. cinnamoneus transconjugation was obtained on mannitol soya flour medium containing 50 mM MgCl2, using 2.5 × 108 Escherichia coli as donor and spores treated with heat treatment at 35°C for 10 min as host. By cloning and sequencing the attB integration site, a single attB site within an open reading frame coding for a pirin homologue was located in S. cinnamoneus genome. Its sequence exhibited the highest degree of sequence similarity with that of Streptomyces clavuligerus. These results provide sufficient efficiency to enable conjugal transfer of genetic elements for S. cinnamoneus, and also should facilitate molecular genetic studies for improvement in production ability of transglutaminase used in food industry.