Abstract
microRNA156 (miR156) is highly conserved across land plants and is best known asthe master regulator of vegetative phase change in angiosperms. In angiosperms, its
temporal decline during development results in increased expression of SQUAMOSA
PROMOTER BINDING PROTEIN-LIKE (SPL/SBP) genes and the production of adult
traits. This transition has been well-characterised in angiosperms where the
sporophyte is the dominant life cycle phase. However, the function of miR156 in early
land plants with a dominant gametophyte is far less explored, leaving unanswered
questions surrounding miR156’s evolutionary origin and contribution to the success of
land plants. While previous research has shown analogous miR156 and SPL temporal
expression patterns between bryophytes and angiosperms, their developmental roles
remain poorly understood. In this thesis, I used GUS reporter fusions to reveal that
SBP3 is repressed by miR156 in both protonemal tissue and the sporophyte.
Furthermore, SBP13 is repressed in gametophore tips and the base of the sporophyte
but not the sporogenic centre. Despite clear spatial regulation, release from
suppression did not result in consistent phenotypic changes, making it difficult to draw
conclusions about the function of miR156. I also present preliminary evidence that P.
patens SBP genes can complement Arabidopsis spl loss-of-function mutants,
supporting the hypothesis that this regulatory network is highly conserved across land
plants. Finally, copper stress experiments in mutant lines did not reveal a role for
miR156-targetted SBP genes in copper homeostasis. Together, my findings suggest
that the miR156-SPL module is a highly conserved network active in both the P. patens
gametophyte and sporophyte, and that it may have contributed to the proliferation and
developmental complexity of the land plant sporophyte.
| Date of Award | 9 Dec 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Jim P Fouracre (Supervisor) & Jill Harrison (Supervisor) |