The flexible chromosomes of fungi

Many fungi do not reproduce sexually. Phytopathology expert Bart Thomma discovered that the Verticillium fungus can manage its genes in a very flexible way despite its celibate existence.

Verticillium is a fungus family that causes wilt in plants such as tomatoes and potatoes. Tomatoes wither as the fungus infects the plant. Wageningen plant scientists have determined the genome sequence of various Verticillium species in recent years. Their research has revealed that the fungi are genetically even more flexible in some respects than sexually reproducing animals and plants.

The norm in nature and Verticilium

Humans have 46 chromosomes, 23 from each parent. The genes for characteristics such as eye colour, for example, are found in the same chromosome for everyone. The number of chromosomes is also the same in other organisms which reproduce sexually. This is the norm in nature as it ensures that the genes of the parents can be combined in the offspring.

Verticilium operates very differently, says professor of phytopathology Bart Thomma. “Each strain of Verticillium we have examined has an even number of chromosomes, but the length varies greatly from individual to individual – a gene will be found on chromosome one in one individual and on chromosome three in another. We long thought that sexual reproduction was necessary for variation but I think asexual organisms have developed other ways to achieve it.

Immune system and Verticilium

“Just like people and animals, plants also have an immune system of sorts. This defence system continuously adapts in order to recognise new pathogens. To succeed, pathogens must therefore adapt very quickly once they are recognised. Verticilium uses its genetic flexibility to adapt to plants that develop defence mechanisms. When resistances are broken, we see that this often occurs in places where the genetic structure has changed.”

Thomma hopes that a better understanding of the agility of Verticillium may lead to new ways of making plants resistant to fungi, allowing chemical pesticides to be deployed less often.