Proline modulates root meristem size and root growth in Arabidopsis thaliana

Beside its role in protein synthesis, proline plays a special role in plants both under stress and non-stress conditions. In most plant species this amino acid accumulates in response to a number of abiotic and biotic stresses, probably as an adaptive mechanism to improve stress tolerance. Under non-stress conditions proline accumulates in reproductive organs and is involved in developmental processes related to reproduction, such as flowering, pollen development and embryogenesis. Recently proline has been shown to modulate root meristem size in Arabidopsis by controlling the ratio between cell division and cell differentiation. The effects of proline on meristem size are parallel to, and independent from, hormonal pathways, and do not involve the expression of genes controlling cell differentiation at the transition zone, such as ARR1, ARR12 and SHY2. On the contrary, proline appears to control specifically cell division in early stages of postembryonic root development, as shown by the expression of the G2/M-specific CYCB1;1 gene. We are currently investigating the molecular and genetic mechanisms through which proline exerts its effects on root development.