Transcriptome analysis reveals improved root hair growth in trifoliate orange seedlings by arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) regulate root hair formation in host plants, whereas the underlying mechanisms are unknown at the molecular level. The present study aimed to analyze the molecular change in trifoliate orange (Poncirus trifoliata) seedlings after inoculated with Clariodeoglomus etunicatum (C_e) and Funneliformis mosseae (F_m) for 3 months. We analyzed RNA sequences in lateral root tips from non-mycorrhizal and mycorrhizal plants, then randomly screened and verified 10 differentially expressed genes (DEGs) using quantitative real-time PCR (qRT-PCR). The results showed that both fungal species increased root hair density and length in all orders of root classes (except 2nd lateral roots in C_e treatment), as well as root biomass and phosphorus (P) content in leaves and roots. We identified 1300 and 1810 DEGs in plants inoculated with C_e and F_m and validated transcriptome data using qRT-PCR, where 21, 19, and 10 DEGs were associated with P, auxins, and expansins, respectively. The most downregulated and upregulated DEGs associated with P encoded acid phosphatase and phosphate transporter, respectively. The ABC transporter was the most upregulated DEG associated with auxin metabolism. Among the DEGs associated with expansins, 50% each were upregulated and downregulated. These findings revealed that mycorrhiza colonization elicited molecular changes in improved root hairs of trifoliate orange in association with phosphorus, auxin, and expansins.