ABA in bryophytes: how a universal growth regulator in life became a plant hormone?

Abstract

Abscisic acid (ABA) is not a plant-specific compound but one found in organisms across kingdoms from bacteria to animals, suggesting that it is a ubiquitous and versatile substance that can modulate physiological functions of various organisms. Recent studies have shown that plants developed an elegant system for ABA sensing and early signal transduction mechanisms to modulate responses to environmental stresses for survival in terrestrial conditions. ABA-induced increase in stress tolerance has been reported not only in vascular plants but also in non-vascular bryophytes. Since bryophytes are the key group of organisms in the context of plant evolution, clarification of their ABA-dependent processes is important for understanding evolutionary adaptation of land plants. Molecular approaches using Physcomitrella patens have revealed that ABA plays a role in dehydration stress tolerance in mosses, which comprise a major group of bryophytes. Furthermore, we recently reported that signaling machinery for ABA responses is also conserved in liverworts, representing the most basal members of extant land plant lineage. Conservation of the mechanism for ABA sensing and responses in angiosperms and basal land plants suggests that acquisition of this mechanism for stress tolerance in vegetative tissues was one of the critical evolutionary events for adaptation to the land. This review describes the role of ABA in basal land plants as well as non-land plant organisms and further elaborates on recent progress in molecular studies of model bryophytes by comparative and functional genomic approaches.

Phytohormones in red seaweeds: a technical review of methods for analysis and a consideration of genomic data

“…In addition, genes encoding 9-cisepoxycarotenoid dioxygenase (NCED), xanthoxin dehydrogenase (XanDH, also known as ABA2), and abscisic aldehyde oxidase (AAO3) involved in ABA biosynthesis from carotenoids (Nambara and Marion-Poll 2005) were also identified in Bangiophycean seaweeds (Mikami et al 2016), although biochemical validation of the enzymatic activity is needed. These findings strongly support the presence of an ABA biosynthetic pathway in Bangiophyceae, which is consistent with a proposal of an ancient evolutionary origin of the ABA biosynthetic pathway (Takezawa et al 2011).…”

Histone Deacetylase Complex1 Expression Level Titrates Plant Growth and Abscisic Acid Sensitivity in Arabidopsis

“…Whether the HDC1 protein is subject to posttranslational regulation and under which conditions should now be explored. The fact that sequence extension from Rxt3 to HDC1 occurred between algae and land plants is interesting as it coincides with the need of plants to adapt to water stress on land and with the promotion of ABA from growth regulator to plant hormone (Takezawa et al, 2011). It is tempting to speculate that the development of HDC1 as an ABA-stat made an important contribution to this evolutionary progress.…”

Fern and Lycophyte Guard Cells Do Not Respond to Endogenous Abscisic Acid

“…Endogenous production of ABA by ferns and lycophytes during drought stress is likely a reflection of the important but lesser discussed role of ABA in enabling cell survival during stress events, as demonstrated across kingdoms and phyla (Shinozaki and Yamaguchi-Shinozaki, 2000;Zocchi et al, 2003;Karadeniz et al, 2006;Li et al, 2011). One possibility is that this ancient stress signal was coopted for enabling cellular survival in a terrestrial environment during the colonization of land by the earliest plants (Takezawa et al, 2011).…”