Biology subjects

Lenhard, M.

Publications and source records attributed to Lenhard, M..

6 recordsLinked to original sources

bioRxiv2025

Genetic and developmental constraints drive parallelism in flower evolution

Evolution repeatedly gives rise to similar phenotypes, suggesting that constraints and biases make some evolutionary trajectories more likely than others, yet the mechanisms underlying this predictability remain poorly understood. Using repeated transitions to self-fertilization in a model Brassicaceae genus, we show that independent reductions in petal size arise from dosage changes at the same pleiotropic growth regulator, JAGGED (JAG). Petal development exhibits particularly high sensitivity to JAG dosage, resulting in organ-specific morphological shifts with minimal effects on other organs and limited pleiotropy. In both selfing species, these changes were drawn from functionally divergent variants whose polymorphism patterns are consistent with long-term maintenance under weak selection. Our results demonstrate how developmental network architecture and the maintenance of functional variation at pleiotropic loci combine to channel evolution toward predictable outcomes.

evolutionary biology↗

bioRxiv2025

Supergene control of chiral development in mirror-image flowers

How genes determine the left-versus right-handed development of chiral structures is a fascinating question. The reciprocal placement of female and male organs on opposite sides of the midline in mirror-image flowers limits selfing and promotes efficient cross-pollination. Here we identify the molecular and developmental basis of floral handedness in butterfly lilies. Female and male organs deflect by a combination of genetically controlled chirality and gravitropism, orienting left and right with respect to an external rather than internal reference axis. Coordinated organ placement is controlled by a hemizygous supergene containing two causal loci, MIR156-R and YUCCA-R, responsible for opposite female and male organ orientation, respectively. This genomic architecture results in differential placement of the supergene alleles on the pollinators and maintenance of the reproductive polymorphism.

plant biology↗

bioRxiv2024

Style deflection is determined by the handedness of phyllotaxis and differential cell elongation in a species with mirror-image flowers

Many animals and plants show left-right (LR) asymmetry. In some animal systems, handedness has a simple genetic basis, which has allowed identifying how handedness is determined at the molecular level, even if its functional relevance often remains unclear. Mirror-image flowers represent an example of LR asymmetry of clear functional significance, with the reciprocal placement of male and female organs in left- versus right-handed flowers promoting cross-pollination. Here, we use the South African geophyte Cyanella alba to study how handedness of its mirror-image flowers is determined and elaborated during development. Inflorescences of C. alba produce flowers with a largely consistent handedness. However, we find that this handedness has no simple genetic basis, and individual plants can switch their predominant handedness between years. Rather, it is the direction of the phyllotactic spiral that determines floral handedness. Cellular analysis combined with biophysical modelling demonstrates that style deflection is driven by increased cell expansion in the adaxial carpel facing the next oldest flower compared to the other adaxial carpel. The more expanding carpel shows transcriptional signatures of increased auxin signaling compared to the less expanding one, and auxin application to the latter can reverse the orientation of style deflection. We propose that a recently described inherent LR auxin asymmetry in the initiating organs of spiral phyllotaxis determines handedness in C. alba, representing a conserved non-genetic mechanism for creating a stable floral polymorphism. This mechanism links chirality across different levels of plant development and exploits a developmental constraint in a core patterning process to produce morphological variation of ecological relevance.

plant biology↗

bioRxiv2023

Lectins in pistils play a key role in self-incompatibility in the heterostylous Linum perenne

Self-incompatibility is one of the mechanisms preventing inbreeding in populations, based on the failure of pollen grains to germinate or of pollen tubes to grow normally in incompatible crosses. A unique model for studying this process are heterostylous species, in which self-incompatibility alleles are closely linked to flower morphological traits. One such species is L. perenne, a classic distylous species with reciprocal herkogamy and complete self-incompatibility strongly linked. The mechanism of self-pollen recognition is poorly understood in most heterostylous species, including L. perenne. As self-incompatibility in other systems is based on protein-protein interactions and many extracellular proteins are glycosylated, one of the possible participants in this process may be lectins. Therefore, we aimed to investigate the lectin activity in pistils and stamens of L. perenne L-morph and S-morph plants and to establish whether these lectins take part in self-incompatibility. We show that pistil-derived galactose-specific Ca2+-independent lectins from the respective other morph can overcome self-incompatibility in heterostylous L. perenne. This may be due to the presence of some lectins that are specific for arabinose and xylose. Our results suggest that lectins participate in signaling pathways for recognition at the pollen-stigma interface and are involved in the regulation of the self-incompatibility process in L. perenne.

plant biology↗

bioRxiv2022

Convergence and molecular evolution of floral fragrance after independent transitions to self fertilization

The study of the independent evolution of similar characters can highlight important ecological and genetic factors that drive phenotypic evolution. The transition from reproduction by outcrossing to self-fertilization has occurred frequently throughout plant evolution. A common trend in this transition is the reduction of flower features in the selfing lineages, including display size, flower signals and pollinators rewards. These changes are believed to evolve because resources invested in building attractive flowers are reallocated to other fitness functions as the pressures to attract pollinators decrease. We investigated the similarities in the evolution of flower fragrance after independent transitions to self-fertilization in Capsella. We identified a large number of compounds that are similarly changed in different selfer lineages, such that the composition of the flower scent can predict the mating system in this genus. We further demonstrate that the emission of some of these compounds convergently evolved based on mutations in different genes. In one of the Capsella selfing lineages, the loss of {beta}-ocimene emission was caused by a mutation altering subcellular localization of the ortholog of TERPENE SYNTHASE 2 without apparent effects on its biosynthetic activity. This mutation appears to have been selected at the early stage of this selfing lineage establishment through the capture of a variant segregating in the ancestral outcrossing population. The large extent of convergence in the independent evolution of flower scent, together with the evolutionary history and molecular consequences of a causal mutation, suggest that the emission of specific volatiles has important fitness consequences in self-fertilizing plants without obvious energetic benefits.

plant biology↗

bioRxiv2018

Adaptive Reduction of Male Gamete Number in a Selfing Species

The number of male gametes produced is critical for reproductive success and varies greatly between and within species1-3. Evolutionary reduction of male gamete production has been widely reported in plants as a hallmark of the selfing syndrome, as well as in humans. Such a reduction may simply represent deleterious decay4-7, but evolutionary theory predicts that breeding systems could act as a major selective force on male gamete number: while large numbers of sperm should be produced in highly promiscuous species because of male-male gamete competition1, reduced sperm numbers may be advantageous at lower outcrossing rates because of the cost of gamete production. Here we used genome-wide association study (GWAS) to show a signature of polygenic selection on pollen number in the predominantly selfing plant Arabidopsis thaliana. The top associations with pollen number were significantly more strongly enriched for signatures of selection than those for ovule number and 107 phenotypes analyzed previously, indicating polygenic selection8. Underlying the strongest association, responsible for 20% of total pollen number variation, we identified the gene REDUCED POLLEN NUMBER 1 affecting cell proliferation in the male germ line. We validated its subtle but causal allelic effects using a quantitative complementation test with CRISPR-Cas9-generated null mutants in a nonstandard wild accession. Our results support polygenic adaptation underlying reduced male gamete numbers.

evolutionary biology↗