The Evolutionary Degeneration of Pollen in Asexual Dandelions

forthcoming

Dandelions (Taraxacum agg.) are one of the most important plants for insects, providing up to 80% of early spring pollen production in meadows. This high pollen production is surprising and unfavourable from the plant’s perspective as most dandelions reproduce asexually (apomixis). Decreased selection on nutritious pollen is therefore expected and would lead to lower production and degenerate (poor) pollen, or even complete male sterility, in the absence of sex. This would have potentially disastrous consequences for the dependent insects, especially in areas of higher latitude (e.g. Sweden) where sexual dandelions are absent. Little is known, however, about the evolutionary effects of asexuality on pollen production, particularly from a genomic point-of-view. We aim to understand how pollen degenerates under asexuality through a combination of phenotypic and genotypic characterisations in sexual and asexual dandelions, including male sterile plants: 1) microscopy and flow cytometry will reveal the effect of asexuality on pollen number, morphology and viability; 2) comparative transcriptomics in pollen, petals, bracts and leaves will reveal pollen-specific genes and if they are down-regulated under asexuality; 3) comparative transcriptomics in anthers will reveal genes necessary for healthy pollen production; 4) comparative genomics using full gene sequences will reveal the rate of deleterious mutation accumulation in pollen-specific genes, for which museum specimens will be unlocked using a customised Hyb-Seq approach. The fellow will fill significant skill gaps in their career through training in gene expression studies, whilst establishing themselves in plant reproductive biology. NoSexPoorPollen will be the first study to compare pollen gene expression in sexual and asexual plants. By combining phenotypic and genomic studies on pollen under asexuality, we provide an impactful and clear indication of the amount of insect food lost in the absence of dandelion sex.