The GID1-Mediated Gibberellin Perception Mechanism Is Conserved in the Lycophyte Selaginella moellendorffii but Not in the Bryophyte Physcomitrella patens

Abstract

In rice (Oryza sativa) and Arabidopsis thaliana, gibberellin (GA) signaling is mediated by GIBBERELLIN-INSENSITIVE DWARF1 (GID1) and DELLA proteins in collaboration with a GA-specific F-box protein. To explore when plants evolved the ability to perceive GA by the GID1/DELLA pathway, we examined these GA signaling components in the lycophyte Selaginella moellendorffii and the bryophyte Physcomitrella patens. An in silico search identified several homologs of GID1, DELLA, and GID2, a GA-specific F-box protein in rice, in both species. Sm GID1a and Sm GID1b, GID1 proteins from S. moellendorffii, showed GA binding activity in vitro and interacted with DELLA proteins from S. moellendorffii in a GA-dependent manner in yeast. Introduction of constitutively expressed Sm GID1a, Sm G1D1b, and Sm GID2a transgenes rescued the dwarf phenotype of rice gid1 and gid2 mutants. Furthermore, treatment with GA 4 , a major GA in S. moellendorffii, caused downregulation of Sm GID1b, Sm GA20 oxidase, and Sm GA3 oxidase and degradation of the Sm DELLA1 protein. These results demonstrate that the homologs of GID1, DELLA, and GID2 work in a similar manner in S. moellendorffii and in flowering plants. Biochemical studies revealed that Sm GID1s have different GA binding properties from GID1s in flowering plants. No evidence was found for the functional conservation of these genes in P. patens, indicating that GID1/DELLA-mediated GA signaling, if present, differs from that in vascular plants. Our results suggest that GID1/DELLA-mediated GA signaling appeared after the divergence of vascular plants from the moss lineage.

The Gibberellin perception system evolved to regulate a pre-existing GAMYB-mediated system during land plant evolution

“…7): The common ancestor of basal land plants before the separation of the mosses had GAMYB-mediated regulation in the proto-tapetal cells (spore sac cells) and spores for spore outer wall formation. At this stage, the GAMYB-mediated regulation of spore outer wall formation was independent of the GA signalling pathway, as the GA signalling pathway had not yet been established 13,14 . Consistent with this hypothesis, it is reported that the disruption of multiple DELLA-like genes in P. patens did not affect the plant's life cycle 14 , and that the disruption of PpCPS/KS, which encodes ent-kaurene synthase, an enzyme essential for GA synthesis in flowering plants, did not result in abnormal spore development 36 .…”

“…During the divergence of basal vascular plants including lycopods from the moss lineage, a GA receptor, GID1 and DELLA repressors were established as key components for GA perception system in association with a functional GA biosynthetic pathway, indicating the occurrence of the entire GA signalling pathway 13,14 . However, the biological function of GA in basal vascular plants has been unclear, as GA treatment does not cause any developmental defects at the vegetative stage, such as increased stem or leaf elongation, in Selaginella 13 . Therefore, we hypothesized that, in such basal vascular plants, GA may be exclusively involved in the outer wall development of microspores via GAMYB.…”

“…2f). Because bioactive GA negatively regulates the expression of some GA biosynthetic genes, including GA3ox, and positively regulates the expression of GAMYB and CYP703A in flowering plants 1,8,13 , we decided to examine the expression levels of these homologues in the presence and absence of GA 4 . Application of GA 4 to the microsporangium suppressed the expression of SmGA3ox, whereas it induced SmGAMYB and SmCYP703C1 (Fig.…”

“…We first examined the expression pattern of PpGAMYBs to estimate the biological function of PpGAMYBs in P. patens, which has no functional GA perception system and GA biosynthetic pathway 13,14 (Fig. 4a,b).…”

“…Previous anatomical and in silico studies suggest that, similar to flowering plants, present-day bryophytes, including mosses, and lycophytes (lycopods) contain sporopollenin-containing outer walls on the surface of their spores and microspores [9][10][11] , and genes encoding CYP703 homologues have been detected in these genomes 12 . Curiously, however, one of the basal vascular plants, Selaginella, contains a functional GA perception system that is mediated by a GA receptor, GIBBERELLIN-INSENSITIVE DWARF1 (GID1), and suppressor proteins (DELLAs), whereas one of the basal land plants, Physcomitrella patens, does not contain this system [13][14][15][16] . These observations led us to speculate that the ancestral land plants developed sporopollenin-containing outer walls on their spores, which protected the spores from dryness and ultraviolet radiation on land, in association with CYP703-like enzymes, and that GA signalling pathway then evolved to control the development of the spore outer wall via the modulation of CYP703-like expressions during the evolution from mosses to lycopods.…”