The Phosphate Transporter1 (PHT1) family of genes plays pivotal roles in the uptake of inorganic phosphate from soils. However, there is no comprehensive report on the PHT1 family in Zea mays based on the whole genome. In the present study, a total of 13 putative PHT1 genes (ZmPHT1;1 to 13) were identified in the inbred line B73 genome by bioinformatics methods. Then, their function was investigated by a yeast PHO84 mutant complementary experiment and qRT-PCR. Thirteen ZmPHT1 genes distributed on six chromosomes (1, 2, 5, 7, 8 and 10) were divided into two paralogues (Class A and Class B). ZmPHT1;1/ZmPHT1;9 and ZmPHT1;9/ZmPHT1;13 are produced from recent segmental duplication events. ZmPHT1;1/ZmPHT1;13 and ZmPHT1;8/ZmPHT1;10 are produced from early segmental duplication events. All 13 putative ZmPHT1s can completely or partly complement the yeast Pi-uptake mutant, and they were obviously induced in maize under low Pi conditions, except for ZmPHT1;1 (p < 0.01), indicating that the overwhelming majority of ZmPHT1 genes can respond to a low Pi condition. ZmPHT1;2, ZmPHT1;4, ZmPHT1;6, ZmPHT1;7, ZmPHT1;9 and ZmPHT1;11 were up-regulated by arbuscular mycorrhizal fungi (AMF), implying that these genes might participate in mediating Pi absorption and/or transport. Analysis of the promoters revealed that the MYCS and P1BS element are widely distributed on the region of different AMF-inducible ZmPHT1 promoters. In light of the above results, five of 13 ZmPHT1 genes were newly-identified AMF-inducible high-affinity phosphate transporters in the maize genome. Our results will lay a foundation for better understanding the PHT1 family evolution and the molecular mechanisms of inorganic phosphate transport under AMF inoculation.

Phosphorus (P) is an essential macronutrient for plant life, although it is frequently not readily available to crops. Arbuscular mycorrhiza fungi (AMF) can improve plant P levels by inducing the expression of some phosphate (Pi) transporters. Symbiotic Pi uptake by Pi transporters is crucial for AMF colonization and arbuscule dynamics. However, the functions of mycorrhiza-inducible maize Pi transporters are largely unclear. We focused on the interaction between the Pi concentration and AMF colonization in maize, and detecting the induction of a Pi transporter. We investigated AMF colonization and arbuscular development in maize under high and low Pi environments. Low Pi increased AMF colonization and promoted arbuscular development. Further measurement of P concentration showed that AMF significantly improved the maize P status under low Pi conditions. Here, we identified the Pi transporter gene, ZmPt9, which was induced by mycorrhiza formation. In addition, ZmPt9-overexpressing roots were difficult to colonize by AMF. Pi response analysis showed that ZmPt9 complements a yeast mutant defective in Pi transporter activity and improves the P concentration in rice. Together, these data indicated that ZmPt9 is a mycorrhiza-inducible Pi transporter gene involved in Pi uptake.

Nucleotide-binding site-leucine-rich repeat (NBS-LRR) domain proteins are immune sensors and play critical roles in plant disease resistance. In this study, we cloned and characterized a novel NBS-LRR gene ZmNBS25 in maize. We found that ZmNBS25 could response to pathogen inoculation and salicylic acid (SA) treatment in maize, and transient overexpression of ZmNBS25 induced a hypersensitive response in tobacco. High-performance liquid chromatography (HPLC) analysis showed that, compared to control plants, ZmNBS25 overexpression (ZmNBS25-OE) in Arabidopsis and rice resulted in higher SA levels. By triggering the expression of certain defense-responsive genes, ZmNBS25-OE enhanced the resistance of Arabidopsis and rice to Pseudomonas syringae pv. tomato DC3000 and sheath blight disease, respectively. Moreover, we found little change of grain size and 1000-grain weight between ZmNBS25-OE rice lines and controls. Together, our results suggest that ZmNBS25 can function as a disease resistance gene across different species, being a valuable candidate for engineering resistance in breeding programs.

Arbuscular mycorrhizal fungi (AMF) can symbiose with many plants and improve nutrient uptake for their host plant. Rhizosphere microorganisms have been pointed to play important roles in helping AMF to mobilize soil insoluble nutrients, especially phosphorus. Whether the change in phosphate transport under AMF colonization will affect rhizosphere microorganisms is still unknown. Here, we evaluated the links of interactions among AMF and the rhizosphere bacterial community of maize (Zea mays L.) by using a maize mycorrhizal defective mutant. Loss of mycorrhizal symbiosis function reduced the phosphorus concentration, biomass, and shoot length of maize colonized by AMF. Using 16S rRNA gene amplicon high-throughput sequencing, we found that the mutant material shifted the bacterial community in the rhizosphere under AMF colonization. Further functional prediction based on amplicon sequencing indicated that rhizosphere bacteria involved in sulfur reduction were recruited by the AMF colonized mutant but reduced in the AMF- colonized wild type. These bacteria harbored much abundance of sulfur metabolism-related genes and negatively correlated with biomass and phosphorus concentrations of maize. Collectively, this study shows that AMF symbiosis recruited rhizosphere bacterial communities to improve soil phosphate mobilization, which may also play a potential role in regulating sulfur uptake. This study provides a theoretical basis for improving crop adaptation to nutrient deficiency through soil microbial management practices.