Moss genetics and the way forward

The moss Physcomitrella patens was originally chosen for the study of gene regulation in plant development [1].Its gametophyte generation is haploid and exhibits an ordered sequence of developmental transitions facilitating the isolation and identification of mutants.The physiology associated with this sequence had been partially characterised in the closely related Funaria hygrometrica and, for example, shown to involve auxin [2] and cytokinin [3].P. patens was preferred to F. hygrometrica because of the invaluable preliminary studies of Engel [4] and the short, approximately 8-week life cycle of P. patens in laboratory conditions.Consequently, pioneers of the P. patens plant model system envisaged using classical forward genetics for the dissection of developmental processes.Since protonemal tissue, the first tissue to be formed from a germinating moss spore, can be propagated vegetatively, the culture of mutants that were abnormal even at an early stage of development presented no problems-although when such mutants were sterile, orthodox genetic analysis was not possible.To circumvent this problem, somatic hybrids were made by protoplast fusion [5].Perhaps the most complete early example of this forward genetics approach involved 15 sterile gametophore overproducing (ove) mutants [6].Somatic hybridisation demonstrated that the ove phenotype is recessive in all but one case, and the ratio of mutant to wild-type postmeiotic segregants from self-fertilised hybrids was consistent with the altered phenotype being the result of a single mutation in each case tested.Recessive mutants were assigned to three complementation groups (oveA, B, and C) and the ratio of ove to wild-type segregants from a selfed oveA/oveB somatic hybrid showed that the two affected genes are unlinked [7].The biochemical basis for the ove phenotype is an increased level of biologically active cytokinins, principally N 6 -(Δ 2 -isopentenyl) adenine [8, 9].However, mapping the ove mutations and identifying the genes affected and their corresponding proteins have yet to be achieved.Forward genetic dissection of a developmental process using somatic hybridisation is compromised when the causal mutations are dominant [10].Thus, it was another three decades before a candidate-gene strategy showed that 8 of 17 chemically-induced nar (1-naphthalene acetic acid and indole-3-acetic acid resistant) strains harbour mutations distributed among the three P. patens homologues of Arabidopsis Aux/IAA (auxin/indole-3-acetic acid) genes [11].Consequently, forward genetic analysis in P. patens was unattractive to most researchers, and their disaffection was exacerbated by the paucity of markers required for effective mapping of new mutations that existed prior to the generation of a genetic linkage map based on numerous molecular markers and anchored to the genome sequence [12].By contrast, the exceptionally high rate of homologous recombination in P. patens [13], comparable to that in Saccharomyces cerevisiae, and the availability of its complete genome sequence [14] led to an explosion of reverse genetics functional studies that exploited these advantages.Recently, however, the speed, accuracy, and modest cost of next-generation DNA sequencing (NGS) have provided a catalyst for mapping and identifying mutations in mutant plants generated by a forward genetics approach.One of the first successful P. patens studies utilised

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.