The Induction of Biochemical and Morphological Mutants in the Moss Physcomitrella Patens

Abstract

Physcomitrella patens is a monoecious, cleistocarpous moss which completes its life cycle under defined conditions in 7 to 8 weeks. Sexual reproduction is readily obtained by culturing gametophytes at 15 to 19 C. Mutants were induced by treatment of either spores or protonemal cells with ethyl methane sulfonate, N‐methyl‐N'‐nitro‐N‐nitrosoguanidine and X‐rays. Thiamine, para‐aminobenzoic acid, niacin and yeast extract auxotrophs were obtained. Growth response to various supplements was studied in the auxotrophic mutants. Five yellow mutants and two morphological mutants were induced. The chlorophyll content of the yellow mutants is reduced 35‐65% of wild type. The self‐sterile, para‐aminobenzoic acid‐dependent mutant was used as the archegonial parent in crosses with a yellow mutant and a morphological mutant. The self‐sterility of the para‐aminobenzoic acid‐requiring mutant appears to be pleiotropically related to the auxotrophic condition, since self‐sterility does not segregate from nutritional dependence in progeny of crosses. On the basis of tests with heterozygous diploids obtained by aposporous regeneration of capsule cells, two mutant alleles were shown to be recessive to their respective wild‐type alleles.

Molecular genetics of Physcomitrella

“…However, in the photograph published by Engel (1968) no such chromosomal blocks can be seen, thus favouring the existence of two chromosomal races. Nevertheless, the Hamburg strain analysed by Reski et al (1994) originates from the culture which Engel (1968) used and is dierent from the isolate Bryan (1957) has used. Therefore, it seems unlikely that the observed dierences in chromosome numbers are due to the use of dierent chromosomal races in Physcomitrella.…”

“…Frequently, clumped chromosomes were detected, resulting in fewer but bigger chromosomal blocks (Reski et al 1994). However, in the photograph published by Engel (1968) no such chromosomal blocks can be seen, thus favouring the existence of two chromosomal races. Nevertheless, the Hamburg strain analysed by Reski et al (1994) originates from the culture which Engel (1968) used and is dierent from the isolate Bryan (1957) has used.…”

“…Chromosomes of mosses, especially of the Funariaceae, are very small and dicult to analyse (Newton 1984). Consequently, dierent chromosome numbers of Physcomitrella have been reported over several decades: von Wettstein (1925) analysed a German isolate and suggested n = 16 (15±18), Bryan (1957) drew 27 mitotic chromosomes from an isolate from Michigan, while Engel (1968) showed with photographs of diakinesis n = 14 in an English isolate. Finally, based on mitotic as well as on meiotic chromosome counts, Reski et al (1994) supported Bryan's (1957) observation of n = 27 chromosomes.…”

“…Likewise, von Wettstein (1924) recognised the great potential of the haploid moss protonemata for genetically dissecting dierentiation processes. These analyses started with mutant induction in Physcomitrium piriforme, Funaria hygrometrica and Physcomitrella patens (Barthelmes 1940; Oehlkers and Bopp 1957;Engel 1968) and culminated in the synopses on the physiology and genetics of cellular dierentiation in Funaria and Physcomitrella (Bopp 1981(Bopp , 1990Cove 1992;Cove and Knight 1993). These classical genetical studies led to the suggestion that the genetic dissection of Physcomitrella could make signi®cant contributions to understanding the evolution of plant development processes (Goldberg 1988;Chasan 1992).…”

Moss as a Model System for Plant Stress Responses

“…However, one moss species, P. patens, has emerged as an excellent model system for undertaking genome-level analyses. Physcomitrella has been studied since the early years of the twentieth century and at the genetic level since 1968, when the first mutants were isolated [11]. First, the cells of a fully differentiated plant retain their totipotency.…”