Spatio-temporal expression of phytoglobin - a determining factor in the NO specification of cell fate.

Plant growth and development rely on the orchestration of cell proliferation, differentiation, and ultimately death. After varying rounds of divisions, cells respond to positional cues by acquiring a specific fate and embarking onto distinct developmental pathways which might differ significantly from those of adjacent cells exposed to diverse cues. Differential cell behaviour is most apparent in response to stress, when some cells might be more vulnerable than others to the same stress condition. This appears to be the case for stem cells which show abnormal features of differentiation and ultimately signs of deterioration at the onset of specific types of stress such as hypoxia and water deficit. A determining factor influencing cell behaviour during growth and development, and cell response during conditions of stress is nitric oxide (NO), the level of which can be regulated by phytoglobins (Pgbs), known scavengers of NO. The modulation of NO by Pgbs can be cell, tissue, and/or organ specific, as revealed by the expression patterns of Pgbs dictated by the presence of distinct cis-regulatory elements in their promoters. This review discusses how the temporal and spatial Pgb expression pattern influences NO-mediated responses and ultimately cell fate acquisition in plant developmental processes.