The Effects of Herbicides Targeting Aromatic and Branched Chain Amino Acid Biosynthesis Support the Presence of Functional Pathways in Broomrape.

It is not clear why herbicides targeting aromatic and branched-chain amino acid biosynthesis successfully control broomrapes-obligate parasitic plants that obtain all of their nutritional requirements, including amino acids, from the host. Our objective was to reveal the mode of action of imazapic and glyphosate in controlling the broomrape and clarify if this obligatory parasite has its own machinery for the amino acids biosynthesis. callus was studied to exclude the indirect influence of the herbicides on the parasite through the host plant. Using HRT - tomato plants resistant to imidazolinone herbicides, it was shown that imazapic is translocated from the foliage of treated plants to broomrape attachments on its roots and controls the parasite. Both herbicides inhibited callus growth and altered the free amino acid content. Blasting of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and acetolactate synthase (ALS) cDNA against the genomic DNA of yielded a single copy of each homolog in the latter, with about 78 and 75% similarity, respectively, to counterparts at the protein level. We also show for the first time that both EPSPS and ALS are active in callus and flowering shoots and are inhibited by glyphosate and imazapic, respectively. Thus leading to deficiency of those amino acids in the parasite tissues and ultimately, death of the parasite, indicating the ability of to synthesize branched-chain and aromatic amino acids through the activity of ALS and EPSPS, respectively.