Genetic analysis of Physcomitrella patens identifies ABSCISIC ACID NON-RESPONSIVE (ANR), a regulator of ABA responses unique to basal land plants and required for desiccation tolerance

Abstract

The anatomically simple plants that first colonized land must have acquired molecular and biochemical adaptations to drought stress. Abscisic acid (ABA) coordinates responses leading to desiccation tolerance in all land plants. We identified ABA nonresponsive mutants in the model bryophyte Physcomitrella patens and genotyped a segregating population to map and identify the ABA NON-RESPONSIVE (ANR) gene encoding a modular protein kinase comprising an N-terminal PAS domain, a central EDR domain, and a C-terminal MAPKKK-like domain. anr mutants fail to accumulate dehydration tolerance-associated gene products in response to drought, ABA, or osmotic stress and do not acquire ABA-dependent desiccation tolerance. The crystal structure of the PAS domain, determined to 1.7-Å resolution, shows a conserved PAS-fold that dimerizes through a weak dimerization interface. Targeted mutagenesis of a conserved tryptophan residue within the PAS domain generates plants with ABA nonresponsive growth and strongly attenuated ABA-responsive gene expression, whereas deleting this domain retains a fully ABA-responsive phenotype. ANR orthologs are found in early-diverging land plant lineages and aquatic algae but are absent from more recently diverged vascular plants. We propose that ANR genes represent an ancestral adaptation that enabled drought stress survival of the first terrestrial colonizers but were lost during land plant evolution.

Evolutionary Conservation of ABA Signaling for Stomatal Closure

“…To identify genes potentially involved in stomatal regulation along the green plant tree of life, we first interrogated a collection of microarray and RNAsequencing (RNA-seq) data sets from the angiosperms Arabidopsis (Leonhardt et al, 2004;Wang et al, 2011) and O. sativa (Lenka et al, 2011), the moss P. patens (Stevenson et al, 2016) and the green algae K. flaccidum (Holzinger et al, 2014). We also conducted qPCR on the fern P. proliferum (Fig.…”

Synteny-based phylogenomic networks for comparative genomics

“…Most of the LEA gene expression during seed development and environmental stresses is regulated via abscisic acid (ABA)-signalling pathways (Galau et al, 1986;Espelund et al, 1992;Shinde et al, 2012;Delahaie et al, 2013;Stevenson et al, 2016). The desiccation-induced LEA gene expression via ABA-responsive pathways is conserved across basal and angiosperm resurrection species (Cuming et al, 2007;Shinde et al, 2012;Stevenson et al, 2016).…”

“…The desiccation-induced LEA gene expression via ABA-responsive pathways is conserved across basal and angiosperm resurrection species (Cuming et al, 2007;Shinde et al, 2012;Stevenson et al, 2016). It seems that the acquisition of new genomic contexts by desiccation-related LEAs of the resurrection monocot Xerophyta viscosa is one important footprint of DT, and suggests that other regulatory mechanisms, likely independent on ABA, may also work to assure protection against desiccation.…”

“…In plants, LEA_4 is strongly associated with DT in basal and angiosperm resurrection species via an anciently conserved ABA signalling pathway (Cuming et al, 2007;Hundertmark and Hincha, 2008;Shinde et al, 2012;Delahaie et al, 2013;Stevenson et al, 2016). Our species set contained two desiccation tolerant species, the bryophyte Physcomitrella patens and the monocot Xerophyta viscosa, however, synteny cannot be detected between these species due to the large evolutionary distance.…”

“…LEAs were originally associated with the acquisition of DT in plant embryos due to the high gene expression and protein accumulation in the later stages of seed maturation (Galau et al, 1986;Dure et al, 1989;Espelund et al, 1992;Manfre et al, 2006;Delahaie et al, 2013). In vegetative tissues, LEAs were found to accumulate upon abiotic stresses such as drought, salinity, heat and freezing, and under desiccation in resurrection plants (Hoekstra et al, 2001;Cuming et al, 2007;Amara, 2014;Stevenson et al, 2016). Interestingly, LEA genes are also found outside the plant kingdom, suggesting a common mechanism of DT across distinct life forms (Browne et al, 2002;Tunnacliffe et al, 2005;Kikawada et al, 2006;Gusev et al, 2014).…”