Abstract
ABSTRACTHistidine kinases (HKs) are among the most prominent sensing proteins studied in the kingdom Fungi. Their distribution and biological functions in early diverging fungi (EDF), however, remain elusive. We have taken advantage of recent genomic resources to elucidate whether relationships between the occurrence of specific HKs in some EDF and their respective habitat/lifestyle could be established. This led to the unexpected discovery of fungal HKs that share a high degree of similarity with receptors for plant hormones (ethylene and cytokinin). Importantly, these phytohormone receptor homologs are found not only in EDF that behave as plant root symbionts or endophytes but also in EDF species that colonize decaying plant material. We hypothesize that these particular sensing proteins promoted the interaction of EDF with plants, leading to the conquest of land by these ancestral fungi.
Highlights
Histidine kinases (HKs) are prominent sensing proteins present in bacteria, amoebae, plants, and fungi
HKs are widespread in the kingdom Fungi, and to date in Dikarya (i.e., Ascomycota and Basidiomycota) they have been reported to be involved in stress adaptation, red light perception, morphogenesis, and virulence [4]
With the exception of a few recent insights into the distribution of these sensing proteins in Mucoromycotina [5], no extensive analysis of HKs has been conducted to date across the so-called early diverging fungal (EDF) lineages, which comprise a large portion of the phylogenetic diversity of the kingdom Fungi though just a small proportion of described species [6,7,8]
Summary
Histidine kinases (HKs) are prominent sensing proteins present in bacteria, amoebae, plants, and fungi. Further BLAST analysis of more than 500 fungal genomes (using the Rhizophagus RiHHK6 ethylene binding domain as the query) led us to identify homologous sequences in several other EDF which are known to colonize plant materials (leaf litter, twigs, decaying fruits, soil) (Table 1), including Conidiobolus (CcHHK3), Catenaria (CaHHK1 and CaHHK2), Gonapodya (GpHHK2), Basidiobolus (Bm|388937|), and Spizellomyces (SPPG_07928) (Fig. 2 and 3A).
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