Parasexuality contributes to diversity and adaptive evolution of haploid (monokaryotic) fungi. However, non-sexual genetic exchange mechanisms are not defined in dikaryotic fungi (containing two distinct haploid nuclei). Newly emerged strains of the wheat stem rust pathogen, Puccinia graminis f. sp. tritici (Pgt), such as Ug99, are a major threat to global food security. Here, we provide genomics-based evidence supporting that Ug99 arose by somatic hybridisation and nuclear exchange between dikaryons. Fully haplotype-resolved genome assembly and DNA proximity analysis reveal that Ug99 shares one haploid nucleus genotype with a much older African lineage of Pgt, with no recombination or chromosome reassortment. These findings indicate that nuclear exchange between dikaryotes can generate genetic diversity and facilitate the emergence of new lineages in asexual fungal populations.

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dtww@ucla.edu.

Hyperlipemia and oxidized LDL (ox-LDL) are important independent cardiovascular risk factors. Ox-LDL has been shown to stimulate vascular smooth muscle cell (VSMC) proliferation. However, the effects of hyperlipemia and the molecular mechanisms mediating hyperlipemia and ox-LDL effects on VSMC growth are poorly understood. The helix-loop-helix (HLH) transcription factor, Id3, is a redox-sensitive gene expressed in VSMC in response to mitogen stimulation and vascular injury. Accordingly, we hypothesize that Id3 is an important mediator of ox-LDL and hyperlipemia-induced VSMC growth. Aortas harvested from hyperlipemic pigs demonstrated significantly more Id3 than normolipemic controls. Primary VSMC were stimulated with ox-LDL, native LDL, sera from hyperlipemic pigs, or normolipemic pigs. VSMC exposed to hyperlipemic sera demonstrated increased Id3 expression, VSMC growth and S-phase entry and decreased p21^cip1 expression and transcription. Cells stimulated with ox-LDL demonstrated similar findings of increased growth and Id3 expression and decreased p21^cip1 expression. Moreover, the effects of ox-LDL on growth were abolished in cells devoid of the Id3 gene. Results provide evidence that the HLH factor Id3 mediates the mitogenic effect of hyperlipemic sera and ox-LDL in VSMC via inhibition of p21^cip1 expression, subsequently increasing DNA synthesis and proliferation.