A transcriptomic perspective of P trade in mycorrhizal grapevine.

Nutrient exchanges are a key feature of arbuscular mycorrhizal (AM) symbiosis. Grapevine (Vitis vinifera), one of the most economically important crops worldwide, relies heavily on AM symbiosis for its growth and development. Since the phylloxera crisis, cultivated grapevines are obtained by grafting a Vitis vinifera scion onto a rootstock. In this study, we investigated the responses of the rootstock "Riparia Gloire de Montpellier" to mycorrhizal root colonization under three distinct phosphate (P) levels. We explored regulatory aspects of plant P nutrition by comparing the transcriptome profiling of non-colonized roots and roots colonized by the AM fungus Rhizophagus irregularis DAOM197198. We have shown that P availability significantly influences gene expression in both the AM fungus and the grapevine. Our transcriptomic study shed light on the molecular mechanisms that prevail during the AM symbiosis of a perennial woody plant species, with available P affecting several functional classes of proteins. The nine genes coding for Pht1 transporters in the R. irregularis genome were either down-regulated (RiPT1 and RiPT2) or up-regulated by the high-P treatment (RiPT8 and RiPT11), up-regulated by the low-P treatment (RiPT5), and regulated in a P-dose-dependent manner (RiPT9 and RiPT10). Expression of two of the three identified AM-induced Pht1, VvPT4 and VvPT8, was enhanced under mycorrhizal conditions, but finely tuned by the P treatment. To immunolocalize VvPT4 and VvPT8, we developed an innovative root-clearing protocol specifically designed for woody plants. This technological advancement has made it possible to visualize only VvPT4 at the periarbuscular membrane of mature arbuscules, its expression being strongly influenced by differences in P availability.