Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Summer 2025

Thesis Director

Barbara Carlsward

Thesis Committee Member

Thomas Canam

Thesis Committee Member

Isaac Slaven

Abstract

In vitro plant regeneration, particularly through organogenesis and somatic embryogenesis, is essential for plant transformation and crop improvement, especially in recalcitrant species like sunflower. In this study, we explore the genetic and molecular mechanisms underlying regeneration in Helianthus eggertii, a wild sunflower species with high regeneration potential. Global gene expression profiling, conducted using Oxford Nanopore sequencing across multiple time points and genotypes, identified sixty-three core differentially expressed genes (DEGs) critical to regeneration. These DEGs are associated with critical biological processes such as cell proliferation, transcriptional regulation, and photosynthesis. Among them, a sunflower WUSCHEL-related homeobox transcription factor (WOX4) showed preferential expression in the shoot meristem, highlighting its pivotal role in meristem activity and shoot formation. Overexpression of H. eggertii WOX4 in both sunflower and tobacco enhanced transformation and regeneration efficiencies, underscoring the gene’s significance in regulating regeneration. Genetic diversity among H. eggertii lines was also observed, with regeneration capacity ranging from 0% to ~ 100%, emphasizing the influence of genotype on regeneration success. These findings provide valuable insights into the molecular regulation of plant regeneration and offer potential strategies for improving in vitro regeneration efficiency in sunflower and other recalcitrant crops, with broader implications for crop transformation and breeding programs.

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