Endogenous Diterpenes Derived from ent-Kaurene, a Common Gibberellin Precursor, Regulate Protonema Differentiation of the Moss Physcomitrella patens      

Abstract

Gibberellins (GAs) are a group of diterpene-type plant hormones biosynthesized from ent-kaurene via ent-kaurenoic acid. GAs are ubiquitously present in seed plants. The GA signal is perceived and transduced by the GID1 GA receptor/DELLA repressor pathway. The lycopod Selaginella moellendorffii biosynthesizes GA and has functional GID1-DELLA signaling components. In contrast, no GAs or functionally orthologous GID1-DELLA components have been found in the moss Physcomitrella patens. However, P. patens produces ent-kaurene, a common precursor for GAs, and possesses a functional entkaurene synthase, PpCPS/KS. To assess the biological role of ent-kaurene in P. patens, we generated a PpCPS/KS disruption mutant that does not accumulate ent-kaurene. Phenotypic analysis demonstrates that the mutant has a defect in the protonemal differentiation of the chloronemata to caulonemata. Gas chromatography-mass spectrometry analysis shows that P. patens produces ent-kaurenoic acid, an ent-kaurene metabolite in the GA biosynthesis pathway. The phenotypic defect of the disruptant was recovered by the application of ent-kaurene or ent-kaurenoic acid, suggesting that ent-kaurenoic acid, or a downstream metabolite, is involved in protonemal differentiation. Treatment with uniconazole, an inhibitor of ent-kaurene oxidase in GA biosynthesis, mimics the protonemal phenotypes of the PpCPS/KS mutant, which were also restored by entkaurenoic acid treatment. Interestingly, the GA 9 methyl ester, a fern antheridiogen, rescued the protonemal defect of the disruption mutant, while GA 3 and GA 4 , both of which are active GAs in angiosperms, did not. Our results suggest that the moss P. patens utilizes a diterpene metabolite from ent-kaurene as an endogenous developmental regulator and provide insights into the evolution of GA functions in land plants.

Insights into the Origin and Evolution of the Plant Hormone Signaling Machinery

“…Interestingly, the orthologs of DELLA and GID1 proteins of P. patens contain no protein-protein interaction regions (DELLA, LExLE, and VHYNP motifs in the DELLA protein and residues Ile-24, Phe-27, and Tyr-31 in the GID1A protein; Supplemental Fig. S2; Murase et al, 2008), which is consistent with previous experimental studies showing that GID1 and DELLA do not interact with each other in P. patens (Hirano et al, 2007;Yasumura et al, 2007;Hayashi et al, 2010). It follows that GA signaling originated after the evolutionary split of bryophytes and land plants (Yasumura et al, 2007).…”

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

“…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 . In the next step, the common ancestor of basal vascular plants before the separation of the lycopsids acquired GA biosynthesis and GA signalling pathways to regulate the pre-existing GAMYB-mediated system, leading to the establishment of the GA signalling pathway via GAMYB.…”

Evolution of growth-promoting plant hormones

“…Possibly, the capacity of ent-kaurene to stimulate the germination of P. patens spores is attributable to a conversion by those spores of entkaurene to the bioactive compound. Further discussion on entkaurene-derived bioactive compounds was recently provided by Hayashi et al (2010).…”