Decision letter: Combining growth-promoting genes leads to positive epistasis in Arabidopsis thaliana

Different individuals of the same species are not usually identical. Humans, for example, have a range of different values for various traits, such as height and weight, and similar variations are seen in other animals and plants. Some of this variation can be explained by the individual animals or plants inheriting different versions of the same gene. Moreover, two or more genes can sometimes interact to produce a bigger (or smaller) effect on given trait than would be expected from combining the effects of each gene. This phenomenon is called epistasis. Leaf size in plants is a trait that is controlled by genes and by the environment. Genes can exert an effect by influencing how often the cells in the leaves divide and by influencing their expansion. In Arabidopsis thaliana, a small plant that has been widely studied by plant biologists, numerous genes influence leaf size. Now, in order to explore epistasis in plants, Vanhaeren, Gonzalez et al. have crossbred 13 Arabidopsis mutants that had leaves that were larger than those found in wild-type plants. The resulting offspring each inherited a different pair of mutant genes: one gene via the male pollen, and the other via the female egg cell. About 39% of the offspring plants had leaves that were even bigger than those of its parents. Moreover, in most cases the increase in leaf size was larger than expected. Vanhaeren, Gonzalez et al. found that three of the 13 genes were responsible for the biggest increases in leaf size. Also, some of the biggest increases were caused by plants inheriting two genes that both caused the cells to divide more. Other large increases in leaf size were caused by interactions between a gene affecting cell division and a gene affecting cell expansion. By uncovering combinations of plant genes that increase leaf size, it might be possible to develop agricultural crops with enhanced yields.