NOVEL SELECTION METHOD

Method for preparing transformed plant cells or organisms. Method for preparing transformed plant cells or organisms comprises first transfecting a population of plant cells, already containing at least one marker protein (MP) that can exert a direct or indirect toxic effect, with at least one nucleic acid sequence (A) together with at least one compound (I) able to reduce expression, amount, activity and/or function of MP. Transfected cells that contain (A) in their genome and, because of the activity of (I) have a growth advantage relative to non-transformed cells are selected, under conditions where MP exerts its toxic effect on non-transformed cells. Independent claims are also included for the following: (1) plant-derived 5-methylthioribose kinase (MRTK) having any of 5 sequences (134-327 amino acids) reproduced; (2) nucleic acid (II) encoding MRTK and having any of 5 sequences (404-1011 nucleotides) reproduced; (3) double-stranded RNA (III) comprising a sense strand (ss) essentially identical with at least part of the sense transcript of nucleic acid that encodes MP and an antisense strand essentially, best completely, complementary with ss; (4) transgenic expression cassette (EC) containing: (a) a promoter (P) functional in plants and a sequence (IV) that encodes (III); or (b) a sequence encoding at least part of MP, linked to P in the antisense orientation; (5) transgenic vector containing EC; and (6) transgenic plant containing (III), EC or the vector of (5), also derived tissue, organs, parts, cells, cell cultures and reproductive material.