Transcriptome analysis of intraspecific competition in Arabidopsis thaliana reveals organ-specific signatures related to nutrient acquisition and general stress response pathways

Using microarrays, we analysed whole-genome expression changes in Arabidopsis thaliana plants subjected to intraspecific competition. The leaf and root transcriptome was strongly altered by competition. Differentially expressed genes were enriched in genes involved in nutrient deficiency (mainly N, P, K), perception of light quality, and responses to abiotic and biotic stresses. Interestingly, performance of the generalist insect Spodoptera littoralis on densely grown plants was significantly reduced, suggesting that plants under competition display enhanced resistance to herbivory.This study provides a comprehensive list of genes whose expression is affected by intraspecific competition in Arabidopsis. The outcome is a unique response that involves genes related to light, nutrient deficiency, abiotic stress, and defence responses.Due to their sessile nature, plants have constantly to adjust to their changing environment. Temperature fluctuations, variation in water content in soil, and pathogen attacks are some of the environmental factors with which plants have to cope. In particular, the presence of plant neighbours often reduces the availability of resources including light, water and nutrients. This struggle for common limited resources, which leads to decrease in growth, survival and fecundity, is defined as ‘competition’. Furthermore, since plants often have passive seed dispersal, competition can occur between plant neighbours from the same species (intraspecific competition) and, even more, from closely related individuals [1].Competition does not only refer to the passive exploitation of limited resources by plants, but also to an active response to interferences caused by neighbours. It is now clearly established that plants are able to detect and interact with neighbours in different manners. Aboveground, the presence of neighbours can lead to a decrease in light intensity and quality available for the plant. Before light resource becomes limiting, plant