Defense or growth -- How plants allocate resources

Pathogens can significantly weaken the fitness of their hosts, sometimes even causing host mortality. Yet considerable variation is found between species in their investment in disease defense. Evolutionary theory predicts that allocation costs regulate this investment, but testing this hypothesis has been challenging.

In a study published in Science, postdoctoral researcher Michael Giolai and Professor of Plant Biodiversity Anna-Liisa Laine from the University of Helsinki used open databases to identify plant defense genes and growth traits in 184 plant species. They found striking variation among plant species in the number of defense genes, which ranged from 44 to 2,256. Examples include asparagus, which has only 72 resistance genes, while one chili variety has as many as 1,095. Laine and Giolai also discovered a negative correlation between defense investment and growth traits in wild plants: the higher that the proportion of a plants' genome is dedicated to defense genes, the lower growth potential it has.

"Our study demonstrates the significant role of allocation costs in the generation and maintenance of biodiversity. The findings also shed light on mechanisms that limit the evolution of defense," explains Michael Giolai.

Allocation costs refer to the trade-off in distributing resources among different life functions. For plants, this means that if a plant uses many resources (like energy and nutrients) to maintain its defenses, this may detract from other functions such as growth. In other words, the plant must balance its resource use, which can lead to a scenario where a strong defense reduces growth potential, or vice versa.

The study also examined cultivated plants that have been bred for specific traits. In these plants, a negative correlation between growth and defense was not observed due to the breeding that reduced natural variation in the genomes of crop plants.

Giolai and Laine's research is an excellent example of the potential of open science. Sequencing the genomes of hundreds of plant species and collecting data on growth traits would be impossible for a single research team. The increase in open data enables new types of research that help us understand interspecies variation in different traits.

"If we want to understand the mechanisms that maintain interspecies trait variation, a multi-species approach like this is essential. The increasing availability of open data enables entirely new levels of investigation into these questions," states Anna-Liisa Laine.