Methods for identifying herbicidal compounds
The invention concerns novel enzymes having an arogenate dehydrogenase activity, in particular arogenate dehydrogenase enzymes of plants, and the genes encoding said enzymes. The inventive arogenate dehydrogenase enzymes catalyze the last stage of the metabolic pathway of tyrosine biosynthesis, and constitute, as such, potential targets of herbicides. Hence the invention also concerns a method for identifying herbicide compounds targeting said enzymes, said herbicide compounds preventing tyrosine biosynthesis by being fixed on said enzymes. The invention further concerns transgenic plants tolerant to herbicide compounds targeting an enzyme involved in the tyrosine biosynthesis pathway, in particular an enzyme involved in the transformation of L-tyrosine prephenate, in particular an arogenate dehydrogenase enzyme. Said plants become tolerant by expression in their tissues of a prephenate dehydrogenase enzyme, said enzyme being insensitive to said herbicide compounds and enabling the plant to synthetize tyrosine despite being treated with said herbicide compounds.
1. A method for identifying a herbicidal compound having as a target an enzyme with arogenate dehydrogenase activity, said method comprising the steps of
(a) preparing at least two samples, each containing an equivalent amount of an arogenate dehydrogenase enzyme in solution;
(b) treating one of the samples with a compound;
(c) measuring the arogenate dehydrogenase activity in each one of said samples;
(d) comparing the activity of the treated sample with the activity of the untreated sample or samples, wherein the compound used in step (b) is identified as being a herbicidal compound when the activity measured in step (c) is significantly less in the treated sample compared to the untreated sample or samples; and
(e) treating plants with the compound identified in step (d) to validate the herbicidal activity of said compound.
2. The method as claimed in claim 1 , wherein the arogenate dehydrogenase enzyme in step (a) is is encoded by SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6 or SEQ ID NO: 8.