Distribution of style and pollen polygalacturonases among distylous and homostylous Turnera and Piriqueta spp. (Turneraceae)

Identification of a gene encoding polygalacturonase expressed specifically in short styles in distylous common buckwheat (Fagopyrum esculentum)

Common buckwheat (Fagopyrum esculentum) is a heteromorphic self-incompatible (SI) species with two types of floral architecture: thrum (short style) and pin (long style). The floral morphology and intra-morph incompatibility are controlled by a single genetic locus, S. However, the molecular mechanisms underlying the heteromorphic self-incompatibility of common buckwheat remain unclear. To identify these mechanisms, we performed proteomic, quantitative reverse-transcription PCR, and linkage analyses. Comparison of protein profiles between the long and short styles revealed a protein unique to the short style. Amino-acid sequencing revealed that it was a truncated form of polygalacturonase (PG); we designated the gene encoding this protein FePG1. Phylogenetic analysis classified FePG1 into the same clade as PGs that function in pollen development and floral morphology. FePG1 expression was significantly higher in short styles than in long styles. It was expressed in flowers of a short-homostyle line but not in flowers of a long-homostyle line. Linkage analysis indicated that FePG1 was not linked to the S locus; it could be a factor downstream of this locus. Our finding of a gene putatively working under the regulation of the S locus provides useful information for elucidation of the mechanism of heteromorphic self-incompatibility.

Sequencing the genomic regions flanking S-linked PvGLO sequences confirms the presence of two GLO loci, one of which lies adjacent to the style-length determinant gene CYP734A50

Primula vulgaris contains two GLOBOSA loci, one located adjacent to the style length determinant gene CYP734A50 which lies within the S -locus. Using a combination of BAC walking and PacBio sequencing, we have sequenced two substantial genomic contigs in and around the S-locus of Primula vulgaris. Using these data, we were able to demonstrate that two alleles of PvGlo ^P as well as PvGlo ^T can be present in the genome of a single plant, providing empirical evidence that these two forms of the MADS-box gene GLOBOSA are separate loci and not allelic as previously reported. We propose they should be renamed PvGLO1 and PvGLO2. BAC contigs extending from each GLOBOSA locus were identified and fully sequenced. No homologous genes were found between the contigs other than the GLOBOSA genes themselves, consistent with their identity as separate loci. Exons of the recently identified style-length determinant gene CYP734A50 were identified on one end of the contig containing PvGLO2 and these genes are adjacent in the genome, suggesting that PvGLO2 lies either within or at least very close to the S-locus. Current evidence suggests that both CYP734A50 and GLO2 are specific to the S-morph mating type and are hemizygous rather than heterozygous in the Primula genome. This finding contrasts classical models of the HSI locus, which propose that components of the S-locus are allelic, suggesting that these models may need to be reconsidered.

Pectin dynamic and distribution of exchangeable Ca2+ in Haemanthus albiflos hollow style during pollen-pistil interactions

In this report, the localization and spatial distribution of two categories of pectin, high and low methylesterified, on the background of dynamic in loosely bound calcium (Ca(2+)) in Haemanthus hollow style were studied before and after pollination. In the style transmitting tract of unpollinated pistil, mainly high-methylesterified pectins were present, both in the transmitting tract epidermis and in the style canal. After pollination, an increase in the level of two investigated categories of pectin was observed, but the amount of high-methylesterified one in each period of time analyzed was permanently higher. Locally, in the regions of the style canal penetrated by pollen tubes, process of pectin de-esterification was initiated. However, pollination caused an increase of loosely bound Ca(2+) level in the style transmitting tract, this process appears to be not linked with pectin de-esterification and possible Ca(2+) release after the lysis of Ca(2+) cross-linked de-esterified pectin. Instead, it seems to be based on Ca(2+) exocytosis from the transmitting tract epidermis cells providing a source of Ca(2+) for pollen tubes growing in Haemanthus hollow style.

Breeding system variation, genetics and evolution in the Turneraceae

We review the genetics and evolution of breeding systems in the Turneraceae. Distyly occurs in seven of 10 genera and 81% of species. The remaining species are homostylous. Polyploid evolution has been significant in Turnera. Approximately 60% of species are polyploid ranging from diploid through decaploid. No relationship between breeding system and polyploidy is evident. The genetics of distyly involves a one-locus two-allele system (S and s). Evidence from crosses with homostylous species and mutants is consistent with the possibility that a "Primula-type" supergene underlies distyly but does not prove this to be the case. A polygalacturonase, and an alpha-dioxygenase specific to the transmitting tissue of short-styled plants both exhibit morph-limited expression in concert with predictions from an evolutionary model. The function of the proteins in distyly, if any, is unknown. We have begun constructing a fine-scale genetic map of Turnera. Two genetic markers lie within 0.2 cm of the distyly locus. This should provide a starting point for positional cloning of the distyly locus and reveal the genetic architecture and molecular basis of distyly.

Inheritance of spontaneous mutant homostyles in Turnera subulata x krapovickasii and in autotetraploid T. scabra (Turneraceae)

To explore the genetic architecture of distyly in Turnera spp., we determined the inheritance and compatibility behaviour of two spontaneous homostyled mutants. A long-homostyled mutant shoot arose on an otherwise short-styled plant that was an artificial hybrid (Turnera subulata x T. krapovickasii) between two diploid distylous species. The mutation appears to be an allele, SH, of the distyly locus with the dominance relationships, S>SH>s, where S confers the short-styled phenotype, SH confers homostyly in SHSH and SHs genotypes, and ss genotypes are long-styled. Aberrant segregation ratios were observed among some crosses and might be the result of pollen competition. Compatibility relationships are consistent with the hypothesis that a gene complex determines distyly. Infrequently, revertant short-styled flowers have appeared on cuttings of the T. subulata x T. krapovickasii mutant and on occasion, short-styled progeny have appeared in crosses where none were expected. A second mutant homostyle was discovered in autotetraploid T. scabra. The mutation is inherited as above, however, tetrasomic inheritance occurs at the locus. This homostyled mutant carries two copies of the SH allele and has the duplex genotype SHSHss. Compatibility relationships were as observed above. The occurrence of homostyled mutants is consistent with the hypothesis that a linked gene complex underlies the inheritance of distyly in Turnera but we cannot discount the hypothesis that an allelic series is responsible.