The global demand for plant-derived products such as feed and food is increasing dramatically. It is hard to fathom, but in the coming decades three billion additional people will have to be fed while less arable land is available. Plants also start to play a major role in supplying a sustainable, CO₂-neutral source for the ever-increasing energy needs.

There is an obvious and urgent need to further increase crop productivity. As yield is the most important trait for breeding, a considerable amount of (eco)physiological research has been conducted on yield performance of crops. In contrast, surprisingly little is known about the molecular networks underpinning crop yield and plant organ size, partly because of its multifactorial nature in which many physiological processes, such as photosynthesis, water and mineral uptake, mobilization of starch and lipid reserves, and stress tolerance determine the resources available to produce new cells, tissues, and organs.

Albeit plant growth and stress tolerance are obviously complex processes, novel approaches collectively called "systems biology" allow us to better understand this complexity. It is our ambition to decipher the molecular networks underpinning yield and organ growth both under standard as well as mild drought stress conditions in Arabidopsis and the C4 crop maize. Systems biology will ultimately provide a holistic view enabling the optimization of plant productivity.