3. Root system architecture in cereals
In cereals, the root system consists of a primary and several seminal roots formed during embryogenesis and post-embryonic lateral and crown roots, representing the root system (Fig 1A). Primary and seminal roots emerge during germination to ensure water and nutrient uptake by the emerging seedling. Short after germination, post-embryonic roots are formed, elaborating sequentially the root system required to exploit limited soil resources and respond to changing environmental conditions. In cereals, primary and seminal roots are either ephemeral and short-lived like in rice or remain functional over the whole life cycle like barley, maize or wheat. The post-embryonic root system is composed of the lateral and crown roots. Crown roots are shoot-borne roots arising from the lower stem nodes of the main shoot and tillers. They are established throughout the development of the plant, resulting finally in the buildup of the majority of the mature root system. Lateral roots are root-borne roots developing from primary, seminal and crown roots; they confer several branching orders of the RSA. Altogether, they contribute to a fibrous root system, typical of the monocots. Up to now, cereals root systems have been studied in different species of cereals, including rice (Oryza sativa ), maize (Zea mays L.), or Pearl millet (Pennisetum glaucum (L.) R. Br.).
Plants can sense the environment and nutrients and readjust their root developmental program to optimize soil’s foraging. This ability to modulate root growth angle toward a specific resource or environmental stimulus shape the RSA. Studying the molecular regulation of the RSA, which is a crucial determinant for plant anchorage, water and nutrient uptake efficiency, and the establishment of plant microorganisms’ communities, promises to improve crop yield.