Arbuscular Mycorrhizal Fungi Modulate Photosynthetic Gene Expression (rbcl, rbcs, psbA, psbD) to Enhance Salinity Tolerance in Pistacia vera

This study investigated the role of arbuscular mycorrhizal fungi (AMF) in mitigating salinity stress in Pistacia vera L. cv. Ohadi. A greenhouse pot experiment was conducted using a randomized complete block design with two factors: Glomus mosseae inoculation (inoculated or non-inoculated) and salinity (control or 12 dS m⁻¹ NaCl). While salinity reduced AMF colonization from 67% to 43%, AMF-inoculated plants consistently exhibited superior performance compared to non-mycorrhizal plants. Salinity stress significantly decreased shoot and root biomass, total chlorophyll content, and net photosynthetic rate (Pn) in both groups. However, AMF symbiosis significantly ameliorated these negative effects, resulting in higher biomass, chlorophyll content, and a notably higher Pn (38.8% increase) under saline conditions. Furthermore, AMF inoculation altered the chlorophyll a/b ratio under salinity, suggesting an adaptive response in light-harvesting. Molecular analysis revealed that while salinity downregulated psbA, psbD, rbcL, and rbcS expression, AMF differentially upregulated psbA (under both conditions), psbD (specifically under salinity), and rbcL (under both conditions). Additionally, AMF improved shoot potassium (K) content and upregulated the expression of the SKOR gene, involved in K+ transport, under both control and saline conditions. These findings demonstrate that AMF symbiosis enhances salinity tolerance in pistachio by improving K nutrition, modulating photosynthetic gene expression, and consequently, maintaining photosynthetic efficiency under stress.