Breakdown of self-incompatibility in a natural population of Petunia axillaris (Solanaceae) in Uruguay containing both self-incompatible and self-compatible plants

Abstract

Many members of the Solanaceae display a type of gametophytic self-incompatibility which is controlled by a single multiallelic locus, called the S-locus. From our previous survey of more than 100 natural populations of Petunia axillaris (a solanaceous species) in Uruguay, we had found that the majority of the populations of subspecies axillaris were comprised of virtually all self-incompatible individuals. The rest were "mixed populations" which contained mostly self-incompatible and some self-compatible individuals. In this study, we examined the self-incompatibility behavior and determined the S-genotypes of 33 plants raised from seeds obtained from one such mixed population, designated U1. We found that 30 of the 33 plants (designated U1-1 through U1-33) were self-incompatible and a total of 18 different S-alleles were represented. To determine the Sgenotypes of the three self-compatible plants (U1-2, U1-16, and U1-22) and the possible causes for the breakdown of their self-incompatibility, we carried out reciprocal crosses between each of them and each of the 18 S-homozygotes (S 1 S 1 through S 18 S 18 ) obtained from bud-selfed progeny of 14 of the 30 self-incompatible plants. For U1-2 and U1-16, we also carried out additional crosses with U1-25 (with S 1 S 13 genotype) and an S 13 S 15 plant (obtained from a cross between an S 13 -homozygote and an S 15 -homozygote), respectively. Based on all the pollination results and analysis of the production of S-RNases, products of S-alleles in the pistil, we determined the S-genotypes of U1-2, U1-16, and U1-22, and propose that the breakdown of self-incompatibility in these three plants is caused by suppression of the production of S 13 -RNase from the S 13 -allele they all carry. We have termed this phenomenon "stylar-part suppression of an S-allele" or SPS.& k w d : Key words Petunia axillaris · Self-incompatibility · Self-compatibility · Stylar-part suppression& b d y :

Gametophytic self-incompatibility in Lycium parishii (Solanaceae): allelic diversity, genealogical structure, and patterns of molecular evolution at the S-RNase locus

“…Alternatively, this plant may be homozygous and possibly self-compatible. This does not necessarily indicate a breakdown of GSI in the L. parishii population, as a low frequency of SC individuals has been reported for other populations with GSI (eg, Tsukamoto et al, 1999;Stone and Pierce, 2005).…”

Segregation Analyses of Partial Self-Incompatibility in Self and Cross Progeny of Solanum carolinense Reveal a Leaky S-Allele

“…In Campanula rapunculoides, analyses of 31 parental families suggested the presence of 3-5 unlinked, mostly recessive genetic modifiers affecting the strength of the SI response (GoodAvila and Stephenson 2002). In P. axillaris, the presence of self-compatible plants has been shown to be due to three different mechanisms: a linked gene that suppresses the expression of a specific S-RNase gene (Tsukamoto et al 2003a), a loss of function on the pollen component of SI (Tsukamoto et al 2003b), and the presence of unlinked modifiers (Tsukamoto et al 1999). The variable strength of SI has been shown in most cases in species with small patchy populations such as weeds (Baker 1965), island colonizers (Bateman 1952;Burd 1994), and populations growing in peripheral habitats (Busch 2005); these populations typically undergo repeated events of colonization and local extinction and usually consist of a small number of individuals and are likely to experience reduced pollinator and mate availability.…”

“…Several studies have also shown that duplication of the S-locus can lead to breakdown of the GSI response (De Nettancourt 1977Stone 2002), specifically the duplication of the pollen-expressed component of the GSI reaction of the Solanaceae (Tsukamoto et al 1999). Our findings, however, are unlikely to be the result of a duplicated pollen determinant of SI because if the pollen component of the S-locus, S-locus F-box protein (Sijacic et al 2004), is duplicated, then an allele carrying such duplication will be rendered fully selfcompatible (Kao and Tsukamoto 2004) and such mutations are not likely to vary the strength of the SI response with floral age or prior fruit development (Good-Avila and Stephenson 2002) as we observed in our previous studies (Stephenson et al 2003;Travers et al 2004).…”

“…Natural populations, however, often exhibit marked phenotypic variation among individuals in the strength of SI (e.g., Levin 1996;Tsukamoto et al 1999;Stephenson et al 2000;Stone et al 2006). The strength of SI is known to be influenced in some species by environmental conditions such as temperature, by internal stylar conditions such as the age of the flowers, by mutations that directly affect the strength of S-alleles (e.g., weak and strong S-alleles), by mutations that render a specific S-allele functionless, and by unlinked genetic modifiers that can affect the strength of S-alleles in the population (see Levin 1996;Stephenson et al 2000;Good-Avila and Stephenson 2002;Tsukamoto et al 2003a,b).…”

NaStEP: A Proteinase Inhibitor Essential to Self-Incompatibility and a Positive Regulator of HT-B Stability inNicotiana alataPollen Tubes

“…Although S-RNase and SLF/SFB define pollen rejection S-specificity, modifier genes unlinked to the S-locus are required for self-incompatibility (SI; Martin, 1968;Ai et al, 1991;Murfett et al, 1996;Tsukamoto et al, 1999).…”