The invention provides methods of identifying herbicidal auxins. The invention further provides auxin-herbicide-resistant plants and genes conferring auxin-herbicide resistance. This invention also provides a method of identifying other proteins that bind picolinate auxins from additional plant species. The invention further provides a method to identify the molecular binding site for picolinate auxins. The invention also includes the use of the picolinate herbicidal auxin target site proteins, and methods of discovering new compounds with herbicidal or plant growth regulatory activity. The invention also includes methods for producing plants that are resistant to picolinate herbicidal auxins. Specific examples of novel proteins associated with herbicide binding include AFB5, AFB4, and SGT1b.