Soil inoculation with symbiotic microorganisms promotes plant growth and nutrient transporter genes expression in durum wheat.

Sergio Saia,Alfonso S Frenda,Dario Giambalvo,Federico Martinelli,Francesco Sunseri,Vito Rappa,Maria Rosa Abenavoli,Paolo Ruisi

doi:10.3389/fpls.2015.00815

Abstract

In a field experiment conducted in a Mediterranean area of inner Sicily, durum wheat was inoculated with plant growth-promoting rhizobacteria (PGPR), with arbuscular mycorrhizal fungi (AMF), or with both to evaluate their effects on nutrient uptake, plant growth, and the expression of key transporter genes involved in nitrogen (N) and phosphorus (P) uptake. These biotic associations were studied under either low N availability (unfertilized plots) and supplying the soil with an easily mineralizable organic fertilizer. Regardless of N fertilization, at the tillering stage, inoculation with AMF alone or in combination with PGPR increased the aboveground biomass yield compared to the uninoculated control. Inoculation with PGPR enhanced the aboveground biomass yield compared to the control, but only when N fertilizer was added. At the heading stage, inoculation with all microorganisms increased the aboveground biomass and N. Inoculation with PGPR and AMF+PGPR resulted in significantly higher aboveground P compared to the control and inoculation with AMF only when organic N was applied. The role of microbe inoculation in N uptake was elucidated by the expression of nitrate transporter genes. NRT1.1, NRT2, and NAR2.2 were significantly upregulated by inoculation with AMF and AMF+PGPR in the absence of organic N. A significant down-regulation of the same genes was observed when organic N was added. The ammonium (NH4+) transporter genes AMT1.2 showed an expression pattern similar to that of the NO3- transporters. Finally, in the absence of organic N, the transcript abundance of P transporters Pht1 and PT2-1 was increased by inoculation with AMF+PGPR, and inoculation with AMF upregulated Pht2 compared to the uninoculated control. These results indicate the soil inoculation with AMF and PGPR (alone or in combination) as a valuable option for farmers to improve yield, nutrient uptake, and the sustainability of the agro-ecosystem.

Highlights

Plants live in the soil engaging a wide range of interaction with soil microorganisms
NRT2/NAR2.2 was strongly downregulated by N fertilization per high-affinity transport system (HATS) functionality but probably through the increase in the availability of NH4+ in fertilized soils. Such as observed in nitrate transporters, we found that in unfertilized conditions, the expression of the HATS AMT1.2 was significantly increased when wheat was inoculated with arbuscular mycorrhizal fungi (AMF)+plant growth-promoting rhizobacteria (PGPR) compared to native microbial inoculum (NAT); a positive, though not significant, effect was observed with inoculation with AMF
The results of the present study showed that soil inoculation with AMF increased plant growth and

Summary

Introduction

Plants live in the soil engaging a wide range of interaction with soil microorganisms. Such interaction can include a benefit, a disadvantage or a null effect on plant growth and nutrient uptake and such an effect depends on soil conditions, especially nutrient availability for the plant and the microorganisms. AMF can provide alternative nutrient uptake pathways (Finlay, 2004), which are important for plant growth when nutrient availability is low. The effects of AMF on the enhancement of P uptake are well known and involve different genes encoding Pht transporters (Javot et al, 2007). The differential expression of two Pi transporter genes (Pht1;3 and Pht1;6) in maize root colonized by different AMF was highlighted (Tian et al, 2013)

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