Individual variability in plants: From intra- to inter-individual variability and its response to the environment

Individual variability refers to the differences observed among genetically identical plants or cells grown in the same environment. Phenotypic and transcriptional variability have been extensively described in unicellular organisms and mammalian cells. However, increasing evidence now points to both intra- and inter-individual variability in plants. Cell-to-cell variability in gene expression within a single plant (intra-individual variability) is now recognised as a key factor contributing to the robustness of plant development as well as environmental responses. At a broader scale, multiple studies strongly suggest that inter-individual variability, often involving gene expression differences between individual seedlings, can be associated with an adaptive value at the population level under challenging environmental conditions. This review first aims to describe what is currently known about intra- and inter-individual variability in plants, with a main focus on gene expression variation and highlighting the importance of chromatin modifications. We then illustrate how the extent of individual variability can differ depending on environmental conditions, and discuss how the plasticity of such variability may enhance the ability of plants to respond to challenging situations. These observations finally underline the relevance of investigating individual variability in the context of agriculture.