Strigolactones inhibit caulonema elongation and cell division in the moss Physcomitrella patens.

Beate Hoffmann,Sandrine Bonhomme,Katia Belcram,Cécile Labrune,Hélène Proust,Catherine Rameau,François-Didier Boyer,Michael M. Meijler

doi:10.1371/journal.pone.0099206

Abstract

In vascular plants, strigolactones (SLs) are known for their hormonal role and for their role as signal molecules in the rhizosphere. SLs are also produced by the moss Physcomitrella patens, in which they act as signaling factors for controlling filament extension and possibly interaction with neighboring individuals. To gain a better understanding of SL action at the cellular level, we investigated the effect of exogenously added molecules (SLs or analogs) in moss growth media. We used the previously characterized Ppccd8 mutant that is deficient in SL synthesis and showed that SLs affect moss protonema extension by reducing caulonema cell elongation and mainly cell division rate, both in light and dark conditions. Based on this effect, we set up bioassays to examine chemical structure requirements for SL activity in moss. The results suggest that compounds GR24, GR5, and 5-deoxystrigol are active in moss (as in pea), while other analogs that are highly active in the control of pea branching show little activity in moss. Interestingly, the karrikinolide KAR1, which shares molecular features with SLs, did not have any effect on filament growth, even though the moss genome contains several genes homologous to KAI2 (encoding the KAR1 receptor) and no canonical homologue to D14 (encoding the SL receptor). Further studies should investigate whether SL signaling pathways have been conserved during land plant evolution.

Highlights

Extant bryophytes are considered as descendants of the first plants that colonized land ca 460–470 million years ago
Strigolactone effects on moss filaments in the light To investigate the cellular effects of SLs on P. patens protonema in the light, we compared the cell length of chloronema and caulonema filaments from wild type (WT) and SL-deficient Ppccd8 mutants in light conditions
Addition of GR24 to the Ppccd8 mutant medium led to a reduction in caulonema cell length, with a size similar to that of the WT (Figure 1B)

Summary

Introduction

Extant bryophytes are considered as descendants of the first plants that colonized land ca 460–470 million years ago. They were able to sustain growth and reproduction in an aerial environment due to their evolutionarily innovative features that could anchor the plant to the soil [1]. In P. patens, haploid spores germinate and the first cells divide, producing chloronema filaments that very rapidly differentiate into a second type of filament, the caulonema. Caulonema filaments contain fewer chloroplasts, show faster apical cell division and ensure filament extension and colonization of the soil, in the light and in the dark [4]. Rhizoid filaments differentiate from the gametophore and ensure soil anchoring and nutrient uptake

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Results

Conclusion