Interspecific reproductive barriers in the tomato clade: opportunities to decipher mechanisms of reproductive isolation

Abstract

The tomato clade within the genus Solanum has numerous advantages for mechanistic studies of reproductive isolation. Its thirteen closely related species, along with four closely allied Solanum species, provide a defined group with diverse mating systems that display complex interspecific reproductive barriers. Several kinds of pre- and postzygotic barriers have already been identified within this clade. Well-developed genetic maps, introgression lines, interspecific bridging lines, and the newly available draft genome sequence of the domesticated tomato (Solanum lycopersicum) are valuable tools for the genetic analysis of interspecific reproductive barriers. The excellent chromosome morphology of these diploid species allows detailed cytological analysis of interspecific hybrids. Transgenic methodologies, well developed in the Solanaceae, allow the functional testing of candidate reproductive barrier genes as well as live imaging of pollen rejection events through the use of fluorescently tagged proteins. Proteomic and transcriptomics approaches are also providing new insights into the molecular nature of interspecific barriers. Recent progress toward understanding reproductive isolation mechanisms using these molecular and genetic tools is assessed in this review.

Unilateral incompatibility gene ui1.1 encodes an S-locus F-box protein expressed in pollen of Solanum species

“…Two wild relatives of cultivated tomato, S. cheesmaniae and S. galapagense, both SC, also lack an SLF-23 ortholog, and their pollen is also rejected on pistils of SI species (16,18). These taxa also lack functional ui6.1 (21).…”

“…Cultivated and wild tomatoes provide a powerful model system to study the mechanisms of reproductive barriers in the Solanaceae (16). They display wide variation in mating systems, both between and within species (17).…”

Genetic Diversity in Tomato (Solanum lycopersicum) and Its Wild Relatives

“…The mating system was extensively studied, using the clade as a model to study its effects on species variation (Bedinger, Chetelat et al 2011). Mating system has played a key role in evolution of wild tomatoes, varying from allogamous self-incompatible, to facultative allogamous, to autogamous and self-compatible (Table 1).…”

Genetic diversity of cultivated and wild tomatoes revealed by morphological traits and SSR markers

“…There are 16 wild species of tomato, including S. habrochaites, S. pennellii, S. pimpinellifolium, S. cheesmaniae, S. galapagense, S. peruvianum, S. corneliomulleri, S. chilense, S. chmielewskii, S. arcanum, S. neorickii, S. huaylasense, S. lycopersicoides, S. ochranthum, S. jugandifolium, and S. sitiens (Knapp et al, 2009;Bedinger et al, 2011). These species in the tomato clade are all diploid with the same chromosome number (2n = 24) and are considered to have evolved primarily by genic changes rather than large-scale chromosomal rearrangements (Anderson et al, 2010).…”