Dissecting seed genetic networks through the evolution of plant life-cycle transitions

McCready, Kirsty ORCID: 0000-0002-1175-5973 (2025). Dissecting seed genetic networks through the evolution of plant life-cycle transitions. University of Birmingham. Ph.D.

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Abstract

The evolution of seeds was a transformative event in land plant history, driving the diversification and ecological dominance of seed plants. While the genetic networks underpinning reproductive development are well-characterized in angiosperms, their conservation and function in earlier-diverging lineages remain poorly understood. This thesis investigates key reproductive regulators in the fern Ceratopteris richardii, a model system bridging the evolutionary gap between bryophytes and seed plants. SPOROCYTELESS/NOZZLE (SPL/NZZ) is a critical regulator of seed development in Arabidopsis thaliana, yet homologous genes are also found in seedless plants. In C. richardii, three SPL-like genes—CrSPLA, CrSPLB, and CrSPLC—were identified. Phylogenetic analysis placed CrSPLB and CrSPLC within the SPL clade, suggesting that SPL function predates the origin of seeds. Expression analyses revealed distinct patterns for each homolog, with CrSPLB showing enrichment in reproductive tissues, aligning with a potential ancestral role in sporangia development. Preliminary RNAi knockdown experiments targeting CrSPLB suggested phenotypic effects, such as increased sporangia number, implicating its role in regulating sporangia development. However, complementation assays in Arabidopsis were unsuccessful, leaving the question of functional conservation open for future research.
To explore broader genetic regulators of reproductive development in C. richardii, weighted gene co-expression network analysis (WGCNA) was employed. This analysis revealed modules of co-expressed genes associated with distinct stages of reproductive development. Modules linked to early reproductive fronds highlighted processes such as transcriptional activation, flavonoid biosynthesis, and structural remodelling. In contrast, modules associated with later reproductive stages emphasized meiosis, DNA repair, and redox homeostasis. These findings suggest conservation of key regulatory pathways, with hub genes such as KNAT3-related and MYB80 pointing to potential parallels with seed plant reproductive networks.
This thesis provides novel insights into the genetic regulation of reproduction in ferns and its evolutionary relevance to seed plant development. By integrating phylogenetic, expression, and network analyses, this work lays the groundwork for future studies on the conservation and divergence of reproductive regulatory networks across land plants.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):