Abscisic acid‐induced gene expression in the liverwort Marchantia polymorpha is mediated by evolutionarily conserved promoter elements

Abstract

Abscisic acid (ABA) is a phytohormone widely distributed among members of the land plant lineage (Embryophyta), regulating dormancy, stomata closure and tolerance to environmental stresses. In angiosperms (Magnoliophyta), ABA-induced gene expression is mediated by promoter elements such as the G-box-like ACGT-core motifs recognized by bZIP transcription factors. In contrast, the mode of regulation by ABA of gene expression in liverworts (Marchantiophyta), representing one of the earliest diverging land plant groups, has not been elucidated. In this study, we used promoters of the liverwort Marchantia polymorpha dehydrin and the wheat Em genes fused to the β-glucuronidase (GUS) reporter gene to investigate ABA-induced gene expression in liverworts. Transient assays of cultured cells of Marchantia indicated that ACGT-core motifs proximal to the transcription initiation site play a role in the ABA-induced gene expression. The RY sequence recognized by B3 transcriptional regulators was also shown to be responsible for the ABA-induced gene expression. In transgenic Marchantia plants, ABA treatment elicited an increase in GUS expression in young gemmalings, which was abolished by simultaneous disruption of the ACGT-core and RY elements. ABA-induced GUS expression was less obvious in mature thalli than in young gemmalings, associated with reductions in sensitivity to exogenous ABA during gametophyte growth. In contrast, lunularic acid, which had been suggested to function as an ABA-like substance, had no effect on GUS expression. The results demonstrate the presence of ABA-specific response mechanisms mediated by conserved cis-regulatory elements in liverworts, implying that the mechanisms had been acquired in the common ancestors of embryophytes.

Archetypal Roles of an Abscisic Acid Receptor in Drought and Sugar Responses in Liverworts

“…Similar assays conducted using Marchantia callus cells (Ghosh et al, 2016a) indicated that overexpression of MpPYL1 cDNA enhanced proEm-GUS and pro4xABRE-GUS expression (Supplemental Fig. S3, A and B).…”

“…We previously showed that ABA-induced gene expression in M. polymorpha is dependent on an ABRE as shown for both the wheat Em promoter and endogenous MpDHN1 promoter (Ghosh et al, 2016a). ABA-induced gene expression by both promoters was inhibited by overexpression of M. polymorpha ABI1A (MpABI1A) encoding group A PP2C, a negative regulator of ABA signaling (Tougane et al, 2010;Ghosh et al, 2016a). Yeast two-hybrid assays indicated that MpPYL1 interacted with MpABI1A (Supplemental Fig.…”

“…B, RT-PCR analysis of RNA isolated from gemmalings treated with 1 mM ABA for 6 h. Primers for MpLEAL1 Mapoly0112s0030 genes by binding to an ABRE (Uno et al, 2000;Fujita et al, 2005). We previously showed that ABA-induced gene expression in M. polymorpha is dependent on an ABRE as shown for both the wheat Em promoter and endogenous MpDHN1 promoter (Ghosh et al, 2016a). ABA-induced gene expression by both promoters was inhibited by overexpression of M. polymorpha ABI1A (MpABI1A) encoding group A PP2C, a negative regulator of ABA signaling (Tougane et al, 2010;Ghosh et al, 2016a).…”

Evolution of the Stomatal Regulation of Plant Water Content

“…Whether these alternative SnRK2-independent ABA signaling pathways play an adaptively relevant role in stomatal function is yet to be determined. The core SnRK2-centric ABA signaling pathway is highly conserved across land plants with all lineages, including those species without stomata, such as liverworts, displaying functional physiological responses to ABA (Ghosh et al, 2016), RCAR/PYR/PYL ABA receptors present in genomes (Hauser et al, 2011), and functional PP2Cs (Tougane et al, 2010). This highly conserved ABA signaling pathway is known to regulate desiccation tolerance mechanisms (Tougane et al, 2010), spore dormancy, and sex determination in nonseed plants , among other processes.…”

Oil body formation inMarchantia polymorphais controlled by MpC1HDZ and serves as a defense against arthropod herbivores

“…To test whether Mp C1HDZ expression is regulated by abiotic stress, we performed RT-qPCR analysis under NaCl and ABA treatments at two time-points, including also other members of the same protein family. Unlike the strong induction observed for Mp DHN1 [54], Mp HDZ expression remained unaltered or were slightly reduced under these experimental conditions (Figure S10).…”