Undergraduate Researcher Brown University Providence, Rhode Island
Body of Abstract: As the human population grows and climate change progresses, it is increasingly important to understand the molecular and cellular mechanisms responsible for food production. HAP2 is a broadly conserved, sperm-expressed, transmembrane protein that drives gamete fusion in Arabidopsis and is thus critical for seed and fruit production in that model species. However, HAP2 and gamete fusion have not been studied in crop plants that produce our food. We used CRISPR-CAS9 to generate hap2 loss-of-function mutants in tomato, Solanum lycopersicum. CRISPR-CAS9 transgenic plants actively producing hap2 mutations are completely sterile: flowers abort by abscission at a specialized structure in the pedicel and fruits fail to initiate. We have established two loss-of-function alleles that we maintain as heterozygous plants; one is an early frameshift, the other an in-frame deletion of 77 N-terminal amino acids. Analysis of genetic transmission in crosses between heterozygous mutants and wild-type plants suggest that mutant alleles completely block sperm function. However, seed-set in those same crosses remain the same as in wild type, suggesting an unknown method of fertilization recovery through pollen tube attraction that may not be limited by the number of synergid cells as in Arabidopsis. We are currently focused on using tomato hap2 mutants to determine the molecular mechanisms for fertilization and activation of fruit development and defining this new fertilization recovery mechanism.