The decision to germinate is regulated by divergent molecular networks in spores and seeds

Abstract

Summary Dispersal is a key step in land plant life cycles, usually via formation of spores or seeds. Regulation of spore‐ or seed‐germination allows control over the timing of transition from one generation to the next, enabling plant dispersal. A combination of environmental and genetic factors determines when seed germination occurs. Endogenous hormones mediate this decision in response to the environment. Less is known about how spore germination is controlled in earlier‐evolving nonseed plants.Here, we present an in‐depth analysis of the environmental and hormonal regulation of spore germination in the model bryophyte Physcomitrella patens (Aphanoregma patens).Our data suggest that the environmental signals regulating germination are conserved, but also that downstream hormone integration pathways mediating these responses in seeds were acquired after the evolution of the bryophyte lineage. Moreover, the role of abscisic acid and diterpenes (gibberellins) in germination assumed much greater importance as land plant evolution progressed.We conclude that the endogenous hormone signalling networks mediating germination in response to the environment may have evolved independently in spores and seeds. This paves the way for future research about how the mechanisms of plant dispersal on land evolved.

Abscisic acid controlled sex before transpiration in vascular plants

“…Several pieces of evidence suggest that ABAmediated stomatal closure reported in the moss species P. patens is not analogous to that observed in seed plants. The first is that P. patens does not exhibit the guard cell-specific expression of an SnRK2 (22,25), which is required for a stomatal response to ABA (SI Appendix, Fig. S6) (26).…”

“…Reconstructed evolution of the interactions between A CE /GA (yellow), ABA (red), SnRK2s (green), and S-type anion channels (blue). Precursors of GA and ABA interact to modulate spore dormancy in mosses (22). It is not yet known whether an SnRK2 is involved in this process (dotted green line), or indeed whether these hormones and signaling pathways influence phenotypes in the most basal extant vascular plant lineage, the lycophytes (dotted lines).…”

Physcomitrella patens Reute mCherry as a tool for efficient crossing within and between ecotypes

“…This procedure is similar to that recently described (Vesty et al . ), but does not use cellophane to plate the spores and is scored only at a fixed time point after inoculation.…”

Evolution of the Stomatal Regulation of Plant Water Content

“…One or more of these requirements for ABA-driven stomatal responses does not occur in nonseed plants. In lycophytes and ferns, native SnRK2s are unable to activate native SLACs , while a functional SnRK2-SLAC pairing, albeit weak, observed in P. patens (Lind et al, 2015) is not specific to the guard cells Vesty et al, 2016) and likely plays a role in nitrate homeostasis. In well-studied angiosperms there is a potent pairing of native SnRK2s and SLACs that are specifically expressed in guard cells (Li and Assmann, 1996;Geiger et al, 2009;Fujii et al, 2011).…”