Sense and Sensibility: Inositol Phospholipids as Mediators of Abiotic Stress Responses

摘要

Phosphoinositides perform a variety of functions within the cell. The polyphosphoinositides, PIP and PIP_2, can regulate the dynamics of the actin cytoskeleton and are involved in vesicle trafficking and the regulation of ion-transport in addition to producing second messengers. In this chapter, we propose that these multifunctional lipids are important in coordinating physiological changes as cells respond and adapt to abiotic stresses. In plants, changes in phosphoinositide metabolism, including increased activity of PI 5-kinase and PLC, have been described for light- and gravistimulation, elicitor responses and hyperosmotic stress. Transient IP_3 signals are generated by PLC-mediated hydrolysis of PIP_2 and can take part in modulating cytosolic Ca~(2+). The frequency and amplitude of Ca~(2+) oscillations may convey downstream specificity of gene expression, which manifest specific stress responses. Furthermore, IP_3 signals can cross plasmodesmata and may thereby mediate coordinated responses throughout a tissue. The vectorial transmission of IP_3 can propagate the stress-induced Ca~(2+) signal. Changes in IP_3 metabolism also can reflect shifts in functional emphasis of phosphoinositides in the cell. Changes in PIP_2 mediate changes in cytoskeletal structure or ion transport that are essential for cells as they respond and adapt to stress. As cells experience stress or energy-limiting conditions, phospholipid metabolism will change from de novo synthesis to head group recycling pathways. Preferential turnover of polyphosphoinositides by inositolpolyphosphate 5'phosphatases would be more energy efficient than PLC hydrolysis and de novo synthesis. In summary, the interplay of PIP_2 and IP_3 during the early steps of signal transduction provides a central mechanism to rapidly sense changing environmental conditions and, at the same time, to initiate long term processes, leading to an appropriate stress response.