Mimulus as a Model System
The genus Mimulus (in the family Phrymaceae, order Lamiales) has been a model plant system for ecological and evolutionary genetics since the 1940’s (Clausen, Keck and Heisey 1940). The properties of Mimulus that continue to inspire and facilitate exciting work in these fields (tremendous ecological and phenotypic diversity, amenability to experimental culture) also make this group of flowering plants ideal for ecological and evolutionary genomics research. Mimulus is phylogenetically well placed for comparative genomic analysis because of its relationships to model systems for floral development (snapdragon; both Lamiales), to crop plants with well developed genomic resources (e.g., tomato, sunflower, lettuce; all Asterids), and to Arabidopsis (both Core Eudicots). Furthermore, a relatively small genome size (~500 Mb) and large map length (~2000cM in M. guttatus complex; Fishman et al. 2002) enable genetic dissection.
Mimulus occurs worldwide, but most of the ~160 species are part of two large radiations centered in western North America (Beardsley and Olmstead, 2002) and Australia (Beardsley et al., 2003). Rapid adaptive divergence appears to be a characteristic of the genus. Most of the taxonomic sections contain species complexes - groups of ecologically and morphologically distinct but inter-fertile species (Vickery, 1978). The genus as a whole contains tremendous phenotypic variation, which is mirrored within each species complex and even within species. Mimulus occupies habitats from desert to aquatic to alpine, includes annual, herbaceous perennial and woody perennial growth forms, and contains both diploid and polyploid taxa. Reproductive traits and pollination systems are particularly diverse, and mating systems range from completely outcrossing to obligately selfing and even obligately asexual.
Mimulus is a superb experimental organism for genetics research. All species are hermaphroditic and self-fertile, facilitating the construction of permanent populations such as inbred lines and recombinant inbred lines (RILs). Fecundity is high, with up to 2000 seeds produced from a single flower. Generation times are as short as 60 days for many species. Importantly, individual plants (even of annual species) are readily propagated clonally for long-term maintenance and replication of permanent mapping populations or unique genotypes.
The genomic resources provided here are primarily from two established study systems, the M. guttatus species complex (2n = 28) and the M. cardinalis species complex (2n = 16). Both systems display tremendous variation in traits directly related to reproductive isolation in the wild, including habitat specialization, floral divergence, and the fertility of hybrids.
The specific resources being developed include:
• Assembled and annotated EST sequences from M. guttatus
• Gene-based markers suitable for comparative genome mapping
• High-density linkage maps for the M. guttatus and M. lewisii using the markers developed above
• Physical maps composed of BAC fingerprint contigs for M. guttatus and M. lewisii anchored to the genetic maps using sequence tagged site (STS) markers.
• Beardsley PM, Olmstead RG (2002) Redefining Phrymaceae: the placement of Mimulus, tribe Mimuleae, and Phryma. American Journal of Botany 89:1093–1102.
• Beardsley PM, Yen A, Olmstead RG (2003) AFLP phylogeny of Mimulus section Erythranthe and the evolution of hummingbird pollination. Evolution 57:1397–1410.
• Bradshaw HD Jr, Otto KG, Frewen BE, McKay JK, Schemske DW (1998) Quantitative trait loci affecting differences in floral morphology between two species of monkeyflower (Mimulus). Genetics 149:367–382.
• Clausen J, Keck DD, Hiesey WM (1940) Experimental studies on the nature of species. I. Effects of varied environments on western North American plants. Carnegie Institute of Washington publ. no. 520.
• Fishman LA, Kelly J, Morgan E, Willis JH (2001) A genetic map in the Mimulus guttatus species complex reveals transmission ratio distortion due to heterospecific interactions. Genetics 159:1701-1716.
• Hiesey WM, Nobs MA, Björkman O (1971) Experimental studies on the nature of species. V. Biosystematics, genetics, and physiological ecology of the Erythranthe section of Mimulus. Carnegie Institute of Washington publ. no. 628.
• Vickery, RK Jr (1978) Case studies in the evolution of species complexes in Mimulus. Evolutionary Biology 11: 405-507.