Proline: A versatile amino acid in the presence of salinity and drought in the Capsicum genus

Proline (Pro) is a low-molecular-weight cyclic amino acid that plays an important role as a source of energy and reducing power and as a source of carbon and nitrogen compounds for plant development. In most plant species, Pro is considered a stress marker. It is also a common compatible solute and is used cumulatively by plants under osmotic stress. The pepper genus, which includes species of great economic importance distributed throughout the world, is the target of different types of stresses, both biotic and abiotic, and Pro plays an important role in tolerance to some of these stresses. In this work, we discuss the general aspects of the metabolism, transport, and different functions of Pro in the Capsicum genus. Special focus is given to critical investigations that should be conducted with respect to Pro accumulation under stress conditions, such as salinity and water deficit.