Kendall Villalobos
Investigating Possible Sex Determination Genes HD-ZIP and TCP1 in Hornworts
Hornworts may be small in size, but their unique biology could reshape how we understand plant reproduction and evolutionary history. A clade of about 220 species, hornworts are one of just three groups of non-vascular land plants (bryophytes), and with a unique U/V sex chromosome system, they offer rare insight into the evolution of dioicy and sexual differentiation. About 40% of hornwort species are dioicous, meaning they produce separate male and female individuals, each with four autosomes and one sex chromosome—either U or V. The evolution of these U/V sex chromosomes and the mechanisms underlying sex determination remain poorly understood. This research focuses on two transcription factors, HD-ZIP and TCP1, located within the putative sex-determining region of the U and V chromosomes across hornwort species. Male and female individuals of Anthoceros angustus, grown on AG media supplemented with 0.1% sucrose, were used for DNA and RNA extraction. We assembled transcriptomes using rnaSPAdes from RNA-seq data generated using Illumina sequencing. HD-ZIP and TCP1 genes were identified via BLAST, and phylogenetic analyses were conducted in Geneious with gene trees constructed in IQ-TREE, including the identified transcripts. We found that HD-ZIP and TCP1 genes in both male and female A. angustus group within the female-associated genes from all other dioicous hornworts. These findings suggest that HD-ZIP and TCP1 may not universally determine sex in hornworts and Anthoceros angustus may rely on an alternative pathway. This is consistent with an inferred monoicous common ancestor of Anthoceros and subsequent reversion to dioicy in A. angustus.
Participating in the Boyce Thompson Institute REU was a transformative experience that marked important personal, academic, and professional milestones. As a first-generation student from a predominantly undergraduate institution (PUI), I had limited exposure to a graduate-level research environment and little knowledge about the graduate school application process. This program gave me my first experience in a diverse lab setting, working alongside PhD students and postdoctoral researchers, and provided invaluable insight into what a future in research could look like. I learned wet lab techniques such as DNA and RNA extraction and cloning, while also expanding my computational skills by using tools for genome assembly, gene comparison, and phylogenetic analysis. These experiences not only strengthened my technical foundation but also deepened my appreciation for how plant biology research is conducted at the genomic level. I am especially grateful to the Li Lab for welcoming me into their research community and for introducing me to hornworts as a unique and valuable model system in plant biology. Working closely with my mentors, Peter Schafran and Tanner Robison, as well as my PI, Fay-Wei Li, showed me how collaborative and supportive a research career can be. Their guidance helped me contribute meaningfully to ongoing projects and develop the confidence to ask more thoughtful scientific questions. My time at BTI has solidified my intention to pursue a PhD in plant evolutionary biology and strengthened my motivation to one day become a professor and mentor future students.