Isoleucine-requiring Nicotiana plant deficient in threonine deaminase

Abstract

Well characterized auxotrophic mutants would greatly assist the genetic manipulation of flowering plants, but such mutants are rare1–3. Moreover, auxotrophic mutants isolated at the plant level4–8 and some of those isolated in cell cultures9 are leaky. The isolation of the first non-leaky auxotrophic mutant, requiring a source of nitrogen in reduced form, was possible by direct selection for chlorate resistance of this rare mutant type10. A different approach, the individual testing of colonies grown from mutagenized haploid cells of Datura11 and Hyoscyam us12, has resulted in cell lines with absolute nutritional requirement. We report here the isolation of an isoleucine-requiring line from haploid cell cultures of Nicotiana plumbaginifolia and the regeneration of diploid plants. These plants have no detectable activity of L-threonine deaminase (EC 4.2.1.16), the first enzyme in isoleucine biosynthesis.