From "Risks from GMOs due to Horizontal Gene Transfer", by Paul Keese:
Antibiotic resistance genes have been introduced to GM plants either as part of the bacterial cloning vectors used for the initial gene constructions or under the control of plant promoters to select for successfully modified cells. The concern is that the presence of antibiotic resistance genes in GM plants could provide a reservoir for the appearance of new drug resistant bacteria through HGT from plants to pathogenic bacteria.
I'm afraid I don't understand the "either ... or" contrast here. As I understand, antibiotic resistance genes are routinely introduced into GM plants with the sole goal: to check what cells have underwent transformation (got the neccessary foreign genes in their genome) and what have not.
I would be grateful to learn what are "initial gene constructions" here, and how does the method using "the control of plant promoters" differ from the first method. Is the purpose of introducing antibiotic resistance genes similar in both cases - to check what cells have underwent transformation? Sorry if the questions are too stupid. Please direct me to relevant Wikipedia pages or articles.