POPULATION COMPOSITION, GENDER SPECIALIZATION, AND THE ADAPTIVE SIGNIFICANCE OF DISTYLY IN LINUM PERENNE (LINACEAE)

John L, Jones T, Kitchen S, Hulke BS. Assessment of biogeographic variation in traits of Lewis flax (Linum lewisii) for use in restoration and agriculture

Lewis flax (Linum lewisii) is widely distributed across western North America and is currently used in native ecosystem restoration. There is also growing interest in de novo domestication of Lewis flax as a perennial oilseed crop. To better understand this species and facilitate both restoration and domestication, we used common gardens to assess biogeographical variation in a variety of seed and growth traits from 37 flax accessions, consisting of 35 wild populations from the Intermountain West region, the pre-variety germplasm Maple Grove (L. lewisii) and the cultivar 'Appar' (L. perenne) and related this variation to collection site geography and climate. Results from linear mixed models suggest there is extensive phenotypic variation among populations of Lewis flax within the Intermountain West. Using a multivariate approach, we identify a key suite of traits that are related to latitude and climate and may facilitate adaptation, including flowering indeterminacy, seed mass and stem number. These traits should be taken into account when considering the release of new germplasm for restoration efforts. We also find that Lewis flax seed contains desirably high amounts of alpha-linolenic acid and is otherwise mostly indistinguishable in fatty acid composition from oil-type varieties of domesticated flax (L. usitatissimum), making it a strong candidate for domestication. This study provides fundamental knowledge for future research into the ecology and evolution of Lewis flax, which will inform its use in both restoration and agriculture.

Isolation of the floral morph-related genes in heterostylous flax (Linum grandiflorum): the genetic polymorphism and the transcriptional and post-transcriptional regulations of the S locus

Heterostylous species have two types of flowers, thrum and pin morphs, and these are controlled by a single diallelic locus designated the 'S locus'; fertilization between these two types of flowers is successful. The S gene and the molecular mechanism by which it operates remain to be uncovered, although heterostyly has been studied since the time of Darwin. We compared transcripts and proteins of the thrum and pin flowers of heterostylous flax (Linum grandiflorum) to characterize the molecular differences between them and to elucidate the molecular machinery of heterostyly. Twelve floral morph-related genes were eventually isolated by an integrated study of subtraction and 2D-PAGE analyses, and four genes, TSS1, LgAP1, LgMYB21 and LgSKS1, were predicted to be related to heterostyly. TSS1, a thrum style-specific gene, showed some features suitable for the S gene. Although its biological function is unclear, TSS1 was expressed only in the thrum style and is probably linked to the S locus. LgMYB21, another thrum style gene, would be involved in floral morphogenesis. LgMYB21 was highly expressed in the thrum style, which is shorter than the pin style, and its overexpression in Arabidopsis reduced pistil length. Furthermore, a comparison of transcript and protein accumulations showed no differences in the mRNA accumulation of some thrum-specific proteins, including LgSKS1, suggesting that these are regulated by floral morph-specific post-transcriptional regulation. The Linum S locus regulates not only S specificity but also many floral phenotypes. Dynamic regulation of transcripts and proteins would be necessary for the pleiotropic function of the Linum S locus.

Pollen flow in the distylous Palicourea fendleri (Rubiaceae): an experimental test of the Disassortative Pollen Flow Hypothesis

The Disassortative Pollen Flow Hypothesis proposed by Darwin postulates that the relative position of anthers and stigmas in distylous flowers enhances pollen flow between flowers of different morphs (legitimate pollination), in comparison to flow between flowers of the same morph (illegitimate pollination). In order to test this hypothesis, we measured pollen transport, mediated by a trained Copper-rumped Hummingbird (Amazilia tobaci), between flowers of the distylous Palicourea fendleri under laboratory conditions. In individual tests, we offered to the hummingbird a pollen donor flower and two emasculated recipient flowers in a controlled sequence. After each foraging bout, we counted the number of pollen grains transported from the donor flower to the stigmas of both recipient flowers. In agreement with Darwin's hypothesis, we found that hummingbirds transport pollen of "pin" flowers in significantly higher numbers to legitimate "thrum" stigmas, even if previously visiting a "pin" flower. However, "thrum" pollen was deposited in greater numbers on illegitimate "thrum" stigmas. We interpret this asymmetry largely as the consequence of floral morphology; pollen flow was greater between anthers and stigmas that exhibit greater spatial matching. In P. fendleri, the position of floral organs along the corolla tube does not always precisely correspond. In our experimental system, the probability that the pollinator extracts a pollen grain from the anther and the probability of self-pollination were both dependent on the type of floral morph. We discuss the relevance of the latter findings in relation to other studies of pollen flow in heterostylous species.