SSRP Abstract

The Investigation of a Hornwort Insertion Line With Rhizoids Specific GFP Expression

Student: Isabel Johnson ’22
Research Mentor: Fay-Wei Li (Cornell University Boyce Thompson Institute: Department of Plant Science)

Hornworts are important in understanding plant evolution from algea but more genetic studies need to be done. This study focused on a strain of hornworts that had a gene that glows under fluorescent light inserted into it’s DNA. Though,this specific strain only glowed in the rhizoids; little root-like structures that hornworts have. To investigate this, we looked closer at the DNA, specifically where the genes that we inserted landed in the DNA. We then compared the genes around this insert to the genes in other hornwort species to try and understand why only the rhizoids were glowing.

Hornworts share an ancestor with vascular plants around 500 million years ago and serves as the keystone for understanding the evolution of all vascular plants known today from their algal ancestors. Hornworts also have a symbiotic relationship with cyanobacteria and contain pyrenoid structures that sequester more carbon than chloroplasts of vascular plants. Doing more research on hornwort genomes will therefore aid in our understanding of these characteristics so that they might be implemented in crop plants to increase agricultural yield. There is not much coverage of hornworts in the literature, so preliminary investigation of these hornwort genomes is needed. This investigation looks at the rhizoids of the model species Anthoceros agrestis after it was bombarded with a plasmid containing the fluorescent gene GFP via a gene gun. Though the plasmid containing GFP was bombarded in all tissue, only the rhizoids of this specific strain fluoresced under UV light. To try and understand this, RT-PCR was performed on rhizoid tissue on the genes surrounding the insert to see if they are being expressed and acting as a promoter for GFP. This test showed the genes present and expressed in rhizoid tissue. The DNA of the strain was also sequenced using Nanopore and Readfish Selective Sequencing to gain longer reads and more depth on our target insertion site. The DNA sequence showed multiple inserts of the GFP gene as well as its promoters. A pairwise comparison of the syntenic relationship of the genes surrounding the GFP insert showed the genes belonging to a very large syntenic block conserved in all the genomes of hornworts. GO enrichment factors of this syntenic block were examined and showed an enrichment of DNA-transcription factors. This leads us to believe that the genes surrounding the GFP insert are epigenetically controlled (i.e., methylation or histone acetylation) which is consistent with these gene’s large synteny and enrichment factors.