PoCHL P expression pattern in Posidonia oceanica is related to critical light conditions

In past decades, meadows of Posidonia oceanica (L) Delile have declined extensively in the Mediterranean basin mainly due to disturbances associated with reduced light availability. To investigate the molecular mechanisms of photoacclimation in this seagrass, we selected the CHL P gene as a marker of plant response to light availability because it is involved in the chlorophylltocopherols biosynthetic pathways. After characterizing the PoCHL P gene, its expression pattern was analyzed in leaves of plants growing in 2 distinct meadows that were previously categorized as disturbed and preserved. Plants were sampled during different seasons and light availability was monitored in the selected meadows over a 1 yr period. PoCHL P expression was also analyzed in leaves of plants that were exposed to controlled light conditions in aquaria. We found that PoCHL P was expressed differentially with respect to leaf developmental stage and that its expression pattern changed rapidly under light conditions far below the compensation value established for P. oceanica. Hence, the recognition of this gene as a reasonable marker of critical light conditions provides an important step towards the functional characterization of stress-related genes in seagrasses.