transgenic organisms are GM, i.e. genetically modified, thus you should know at least the sequence of the transgene (the gene transferred into the organism)

A transgene is a gene which is introduced to a host’s genome which does not normally carry that gene. The host is now a GM organism. So, theoretically any gene can be used as a transgene. So, there is not a specific transgene or sequence.

that’s rigth, but you should know sequence of your transgene 🙂

not sure, whether is it what you mean, but you can produce your protein of interest in some other organism in large amounts and then use it for the immunoprecipitation…

Report genes: selectable genes that tell you that the construct has been successfully transferred. Might not have any interest from the point of view of the final product, but convenient in the construction stage. ie antibiotic resistance gene that will allow selection of the plasmid as it is transferred from bacteria to plant during the cloning process.

transgene: your gene of interest. Not necessarily selectable. ie the gene(s) conferring a new metabolic pathway in your final organism are likely to be inactive in a bacterial genome and will not provide any selectable marker to know which of the bacteria has incorporated your plasmid at each of the construction stage.