Group A PP2Cs evolved in land plants as key regulators of intrinsic desiccation tolerance

Abstract

Vegetative desiccation tolerance is common in bryophytes, although this character has been lost in most vascular plants. The moss Physcomitrella patens survives complete desiccation if treated with abscisic acid (ABA). Group A protein phosphatases type 2C (PP2C) are negative regulators of abscisic acid signalling. Here we show that the elimination of Group A PP2C is sufficient to ensure P. patens survival to full desiccation, without ABA treatment, although its growth is severely hindered. Microarray analysis shows that the Group A PP2C-regulated genes exclusively overlap with genes exhibiting a high level of ABA induction. Group A PP2C disruption weakly affects ABA-activated kinase activity, indicating Group A PP2C action downstream of these kinases in the moss. We propose that Group A PP2C emerged in land plants to repress desiccation tolerance mechanisms, possibly facilitating plants propagation on land, whereas ABA releases the intrinsic desiccation tolerance from Group A PP2C regulation.

Plant Raf-like kinase integrates abscisic acid and hyperosmotic stress signaling upstream of SNF1-related protein kinase2

“…ABA-induced activation of the protein kinase corresponding to the expected size of SnRK2 (39 kDa) has been demonstrated recently in P. patens protonemata by in-gel kinase assays using histone IIIS as a substrate (20). We found that protonemata of The protonemata of the lines used in B were bombarded with the Em-GUS and Ubi-LUC constructs and incubated with or without 10 μM ABA for 1 d, followed by the GUS and LUC assays.…”

“…Transcriptome Analysis. Microarray analysis was carried out using a P. patens custom oligonucleotide microarray in which 33,942 gene-specific probes were mounted in an Agilent format microarray as described previously (20). Protonemata of the WT line and AR7 cultured on normal BCDAT medium or medium containing 10 μM ABA for 6 h were used for RNA extraction.…”

“…A twofold expression cutoff was considered to determine the genes decreased in AR7. ABA-regulated genes used for the analysis were described previously (20). The microarray data were deposited in Gene Expression Omnibus (accession GSE68914).…”

“…A recent study also indicated a role of group A PP2Cs as negative regulators of ABA signaling in bryophytes. A transgenic line lacking both group A PP2C genes (PpABI1A and PpABI1B) exhibited constitutive desiccation tolerance with the accumulation of a number of stress-associated transcripts regardless of ABA treatment (20). In this knockout line, however, SnRK2 was activated by exogenous ABA in a manner similar to that in the WT line (20), indicating group A PP2Cs have a minor role in the regulation of SnRK2 and the presence of a previously unidentified mechanism for its activation.…”

Can mosses serve as model organisms for forest research?

“…P. patens is dehydrationtolerant but can become desiccation-and freezing-tolerant by pre-treatment with ABA (Khandelwal et al 2010;Nagao et al 2005). Whereas abiotic stress signaling seems largely conserved between mosses and flowering plants (Khandelwal et al 2010;Komatsu et al 2013;Richardt et al 2010), several studies report on so-called orphan, non-characterized stress responsive moss genes and proteins (Beike et al 2015b;Cui et al 2012).…”