Conditioning plants for arbuscular mycorrhizal symbiosis through DWARF14-LIKE signalling

Abstract

The evolutionarily ancient α/β hydrolase DWARF14-LIKE (D14L) is indispensable for the perception of beneficial arbuscular mycorrhizal (AM) fungi in the rhizosphere, and for a range of developmental processes. Variants of D14L recognise natural strigolactones and the smoke constituent karrikin, both classified as butenolides, and additional unknown ligand(s), critical for symbiosis and development. Recent advances in the understanding of downstream effects of D14L signalling include biochemical evidence for the degradation of the repressor SMAX1. Indeed, genetic removal of rice SMAX1 leads to the de-repression of symbiosis programmes and to the simultaneous increase in strigolactone production. As strigolactones are key to attraction of the fungus in the rhizosphere, the D14L signalling pathway appears to coordinate fungal stimulation and root symbiotic competency. Here, we discuss the possible integrative roles of D14L signalling in conditioning plants for AM symbiosis.

KARRIKIN INSENSITIVE2 regulates leaf development, root system architecture and arbuscular‐mycorrhizal symbiosis in Brachypodium distachyon

“…This suggests that the initiation of root colonisation is blocked, but there is no strict block on progression of colonisation once it is initiated. KAI2‐dependent signalling may condition the root into a state permissive for fungal colonisation (Hull et al., 2021) by reducing SMAX1 levels and thereby increasing expression of SL biosynthesis and the common symbiosis genes (Choi et al., 2020). This may boost hyphopodium formation and symbiotic commitment of the plant host.…”

Strigolactones are chemoattractants for host tropism in Orobanchaceae parasitic plants

“…Indeed, in the case of rice, ~40% of the plant’s nitrogen requirement can be acquired by AMF 58 . It is possible that, in Orobanchaceae parasites, the primary nitrogen source may have shifted from AMF to host plants, potentially by evolving KAI2-mediated signalling via MAX2 59 . Consistently, P. japonicum effectively transfers nitrogen from hosts, especially in nutrient-deficient conditions 60 .…”

KIN3 impacts arbuscular mycorrhizal symbiosis and promotes fungal colonisation in Medicago truncatula

“…Second, KIN3 is as part of a system that regulates permissiveness to AM colonisation in response to plant nitrogen status. As KIN3 is not significantly expressed in uncolonised roots (Figure 5a), we do not believe it functions in the formation of a ‘permissive state’ for colonisation, but rather in autoregulation or sanctioning of the fungus, perhaps directly at the level of the individual arbuscule (Hull et al., 2021). The functionality or cell‐specific nature of action of KIN3 was not tested in this study, but the role of the highly conserved SPARK domain of unknown function and identification of kinase targets are key questions for further work (Montero et al., 2021).…”