Fruit development and diversification.

The evolutionary success of angiosperms depends largely on the unique feature of producing fruits, which protect and nourish the seeds, and at maturity facilitate efficient seed dispersal. Fruits have long been an important energy source for humans, providing us with nutritious proteins and vitamins. Domestication of fruit and seed crops ignited the formation of modern civilisation during the Neolithic Revolution. In the past two decades, the fruit development process has been extensively studied in the model species Arabidopsis thaliana and related Brassicaceae species, and great advances have been made in dissecting the molecular circuit underlying patterning of the fruit into specific tissues. The aim of this Primer is to discuss the molecular network and the inter-connected hormonal signalling events in fruit patterning from an evolutionary and developmental point-of-view. An interesting theme emerging from the studies in leaves and fruits is that tissue polarity, as manifested by anisotropic growth, is tightly associated with local auxin distribution. We further highlight that changes in cell anisotropic growth, possibly directed by the formation of local auxin maxima, may explain fruit-shape diversification in the Brassicaceae.