Opposite lipid signaling pathways tightly control proline accumulation in Arabidopsis thaliana and Thellungiella halophila
Throughout evolution, plants have developed various strategies to tolerate water stress. Among them, the accumulation of proline has been reported in a wide range of species. The metabolic pathway of this compatible solute is relatively well characterized in Arabidopsis thaliana. However, the signaling cascades involved in its regulation remain largely unknown. Thellungiella halophila, which is a close relative of Arabidopsis, tolerates extreme salinity up to 500 mM NaCl. In this work, the involvement of lipid signaling pathways in the regulation of proline accumulation was investigated in these two species upon water stress. A pharmacological approach has been performed using specific inhibitors of key signaling elements. The effects of these inhibitors have been investigated on proline accumulation. The present data show that phospholipases D (PLDs) are negative regulators of proline anabolism under normal conditions inA. thaliana. When such PLD-mediated regulation is abolished by 1-butanol, plants show a higher proline responsiveness to osmotic stress. In contrast to Arabidopsis, 1-butanol does not have any effect on proline accumulation in T. halophila under non-stress conditions. However, upon water constraints, 1-butanol reduces rather than increase proline accumulation. Our data suggest the involvement of a PLD-mediated signaling pathway in the tight regulation of proline metabolism that acts in a opposite way in A. thaliana and T. halophila. On the other hand, phospholipases C exert a positive control on proline accumulation in A. thaliana upon salt stress and a negative control in T. halophila upon water stress and non-stress conditions. In conclusion, we provide experimental evidence that positive and negative regulators are involved in the fine regulation of proline metabolism upon moderate water stress. Our study has defined a critical role of lipid signaling pathways in proline accumulation in A. thaliana and in T. halophila. Thus, in Arabidopsis, our data indicate that PLC-based signaling is a committed step in proline biosynthesis upon salinity but not upon hyperosmotic stress.
KeywordsSalt Stress Phosphatidic Acid Proline Accumulation Hyperosmotic Stress Proline Biosynthesis
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