The Role of Soil Fungi in K+ Plant Nutrition

Abstract

K+ is an essential cation and the most abundant in plant cells. After N, its corresponding element, K, is the nutrient required in the largest amounts by plants. Despite the numerous roles of K in crop production, improvements in the uptake and efficiency of use of K have not been major focuses in conventional or transgenic breeding studies in the past. In research on the mineral nutrition of plants in general, and K in particular, this nutrient has been shown to be essential to soil-dwelling-microorganisms (fungi, bacteria, protozoa, nematodes, etc.) that form mutualistic associations and that can influence the availability of mineral nutrients for plants. Therefore, this article aims to provide an overview of the role of soil microorganisms in supplying K+ to plants, considering both the potassium-solubilizing microorganisms and the potassium-facilitating microorganisms that are in close contact with the roots of plants. These microorganisms can influence the active transporter-mediated transfer of K+. Regarding the latter group of microorganisms, special focus is placed on the role of endophytic fungus. This review also includes a discussion on productivity through sustainable agriculture.

Fungal taste for minerals: the ectomycorrhizal fungusPaxillus involutustriggers specific genes when extracting potassium from different silicates

“…In the presence of K-vermiculite, the fungus was able to derive the K by its displacement from the interlayer sites of vermiculite by other cations in the medium, which is an exchenge mechanism similar to how fungi obtain minerals in soil environments [48]. This suggests that the fungus was not subjected to the same level of K deprivation as with the other two minerals.…”

“…Many soil environments can be cation-poor and therefore the ability of P. involutus to access K from minerals would give an ecological advantage. Therefore, the fungi might have even evolved specific cellular and metabolic mechanisms [48, 63]. An adaptation of the fungi to low K conditions could help to explain the observed down regulation of many genes in the positive control microcosms experiments.…”

Fungal Shaker-like channels beyond cellular K+ homeostasis: A role in ectomycorrhizal symbiosis between Hebeloma cylindrosporum and Pinus pinaster

“…As has recently been revealed, K + acquisition in higher fungi seems to be mediated by membrane transport proteins belonging to the Trk/Ktr/HKT and KT/KUP/HAK families [ 4 , 43 ]. In addition, ACU ATPases have been reported as being involved in K + and Na + uptake in Ustilago maydis , and more generally envisioned as key players of K + transport in fungi [ 7 , 44 ]. PAT ATPases could emerge as mechanisms for absorption of these cations as well, but they have not been studied thoroughly [ 45 , 46 ].…”

“…As a consequence, productivity of agricultural and agroforestry ecosystems is strongly dependent on large and regular addition of chemical fertilizers [3]. Plants developed various strategies to overcome this lack of K + availability and to improve its uptake, such as expression of highaffinity transport systems, exudation of organic acids by the root system, and symbiotic associations with soil-living microbes (reviewed in [4][5][6][7]).…”

Facultative symbiosis with a saprotrophic soil fungus promotes potassium uptake in American sweetgum trees

“…The multiple alignments of the predicted amino acid sequences of ACU, HAK and SKC from several basidiomycetous fungi (Table S4) were performed by using Multiple Sequence Alignment of DNAMAN software 6.0. The ACU family is so far exclusive to fungi, while the HAK transporter and SKC channel are present in both fungi and plants (Haro & Benito, 2019). Therefore, we constructed the phylogenetic trees using the neighbour-joining method (MEGA version 6.0) to reveal the genetic relatedness of the three genes from C. hobsonii with those from other organisms.…”