Synergy of arbuscular mycorrhizal symbiosis and exogenous Ca(2+) benefits peanut (Arachis hypogaea L.) growth through the shared hormone and flavonoid pathway

Peanut yield is severely affected by exchangeable calcium ion (Ca(2+)) deficiency in the soil. Arbuscular mycorrhizal (AM) symbiosis increases the absorption of Ca(2+) for host plants. Here, we analyzed the physiological and transcriptional changes in the roots of Arachis hypogaea L. colonized by Funneliformis mosseae under Ca(2+)-deficient and -sufficient conditions. The results showed that exogenous Ca(2+) application increased arbuscular mycorrhizal fungi (AMF) colonization, plant dry weight, and Ca content of AM plants. Simultaneously, transcriptome analysis showed that Ca(2+) application further induced 74.5% of differentially expressed gene transcripts in roots of AM peanut seedlings. These genes are involved in AM symbiosis development, hormone biosynthesis and signal transduction, and carotenoid and flavonoid biosynthesis. The transcripts of AM-specific marker genes in AM plants with Ca(2+) deprivation were further up-regulated by Ca(2+) application. Gibberellic acid (GA(3)) and flavonoid contents were higher in roots of AM- and Ca(2+)-treated plants, but salicylic acid (SA) and carotenoid contents specifically increased in roots of the AM plants. Thus, these results suggest that the synergy of AM symbiosis and Ca(2+) improves plant growth due to the shared GA- and flavonoid-mediated pathway, whereas SA and carotenoid biosynthesis in peanut roots are specific to AM symbiosis.