Genome-Wide Analysis of the PHT Gene Family and Its Response to Mycorrhizal Symbiosis in Tomatoes under Phosphate Starvation Conditions

Phosphate is one of the essential mineral nutrients. Phosphate transporter genes (PHTs) play an important role in Pi acquisition and homeostasis in tomato plants. However, basic biological information on PHT genes and their responses of symbiosis with arbuscular mycorrhizal in the genome remains largely unknown. We analyzed the physiological changes and PHT gene expression in tomatoes (Micro-Tom) inoculated with arbuscular mycorrhizal (AM) fungi (Funneliformis mosseae) under different phosphate conditions (P1: 0 µM, P2: 25 µM, and P3: 200 µM Pi). Twenty-three PHT genes were identified in the tomato genomics database. Protein sequence alignment further divided the 23 PHT genes into three groups, with similar classifications of exons and introns. Good colonization of plants was observed under low phosphate conditions (25 µM Pi), and Pi stress and AM fungi significantly affected P and N accumulation and root morphological plasticity. Moreover, gene expression data showed that genes in the SlPHT1 (SlPT3, SlPT4, and SlPT5) gene family were upregulated by Funneliformis mosseae under all conditions, which indicated that these gene levels were significantly increased with AM fungi inoculation. None of the analyzed SlPHT genes in the SlPH2, SlPHT3, SlPHT4, and SlPHO gene families were changed at any Pi concentration. Our results indicate that inoculation with AM fungi mainly altered the expression of the PHT1 gene family. These results will lay a foundation for better understanding the molecular mechanisms of inorganic phosphate transport under AM fungi inoculation.