Arbuscular mycorrhizal symbiosis alters the expression patterns of three key iron homeostasis genes, ZmNAS1, ZmNAS3, and ZmYS1, in S deprived maize plants

Abstract

Nicotianamine is an essential molecule for Fe homeostasis in plants, its primary precursor is the S-containing compound methionine, and it is biosynthesized by the enzyme family of nicotianamine synthases (NASs). In maize, a graminaceous plant that follows Strategy II for Fe uptake, ZmNAS genes can be subgrouped into two classes, according to their roles and tissue specific expression profiles. In roots, the genes of class I provide NA for the production of deoxymugineic acid (DMA), which is secreted to the rhizosphere and chelates Fe(III). The Fe(III)-DMA complex is then inserted to the root via a ZmYS1 transporter. The genes of class II provide NA for local translocation and detoxification of Fe in the leaves. Due to the connection between S and Fe homeostasis, S deficiency causes Fe deprivation responses to graminaceous plants and when S is supplied, these responses are inverted. In this study, maize plants were grown in pots with sterile river sand containing FePO4 and were inoculated with the mycorrhizal fungus Rhizophagus irregularis. The plants were grown under S deficient conditions until day 60 from sowing and on that day sulfate was provided to the plants. In order to assess the impact of AM symbiosis on Fe homeostasis, the expression patterns of ZmNAS1, ZmNAS3 (representatives of ZmNAS class I and class II), and ZmYS1 were monitored before and after S supply by means of real time RT-PCR and they were used as indicators of the plant Fe status. In addition, total shoot Fe concentration was determined before and after S supply. AM symbiosis prevented Fe deprivation responses in the S deprived maize plants and iron was possibly provided directly to the mycorrhizal plants through the fungal network. Furthermore, sulfate possibly regulated the expression of all three genes revealing its potential role as signal molecule for Fe homeostasis.

The arbuscular mycorrhizal fungus Rhizophagus irregularis uses a reductive iron assimilation pathway for high‐affinity iron uptake

“…The function of RiFRE1, RiFTR1 and RiFTR2 was also addressed by analysing their expression in the IRM developed in carrot root organ cultures and in maize pot cultures. The finding that RiFTR1 is highly expressed in the IRM indicates that this protein also plays a key role in Fe uptake during the in planta phase of the fungus, which is puzzling since AM fungi are expected to transfer Fe to the plant (Liu et al, 2000;Chorianopoulou et al, 2015). Upregulation of RiFTR2 expression in the IRM of the maize plants grown under low Fe conditions indicates that under these limiting conditions, the fungus needs to increase its cytosolic Fe levels to support its intraradical growth.…”

“…In return, the plant provides the fungus with the carbon compounds it needs to complete its life cycle. Although the main benefit of the AM association is an improved P status of the mycorrhizal plant, AM fungi also play a role in Fe nutrition of their host plants (Clark and Zeto, 1996;Liu et al, 2000;Chorianopoulou et al, 2015). Direct evidence of the capability of the extraradical mycelium (ERM) to take up Fe from the soil and to transfer it to the host plant comes from studies using 59 Fe as a tracer in compartments only accessible by the external hyphae (Caris et al, 1998;Kobae et al, 2014).…”

“…The effect of the AM symbiosis on Fe transport related genes has been addressed in maize, a plant that uses a Fe uptake Strategy II (Kobae et al, 2014;Chorianopoulou et al, 2015). Despite the fungal contribution to Fe uptake, expression of ZmYS1 encoding the transporter that mediates the uptake of PS-Fe(III) complexes from the rhizosphere was not affected in mycorrhizal roots.…”

Possible Roles of Rhizospheric and Endophytic Microbes to Provide a Safe and Affordable Means of Crop Biofortification

“…Recently, mycorrhizal inoculation in wheat roots was reported to have increased the uptake of P, Fe, and Zn by the plant, along with greater root length and density [44]. In maize, the symbiosis of mycorrhiza alters the expression patterns of three key iron homeostasis genes in sulfur-deprived plants, which indicates sulfur works as a signaling molecule for Fe homeostasis [152,153]. The recent growing evidence on the beneficial effects of endophytes suggests that the current knowledge on endophytes could be only the tip of the iceberg.…”

Effects of CO₂ and O₃ on the interaction between root of woody plants and ectomycorrhizae

“…Most tree species create symbiotic relationships with ECM fungi to survive in diverse harsh conditions through an efficient nutrient uptake by ECM fungi (Nara et al 2003;Qu et al 2010;Chorianopoulou et al 2015). For instance, in nutrient impoverished soils, ECM fungi preferentially provide nutrients, like phosphorus (P), and water to the above-ground parts of the host trees rather than the direct absorption by the root tissues (Wallander 2000;Alves et al 2010;Chorianopoulou et al 2015). Therefore, ECM trees absorb more organic P and N than non-ECM trees, since ECM fungi produce ectoenzymes (van der Heijden and Sanders 2002; Choi et al 2005;White and Hammond 2008).…”