UC San Diego

In Arabidopsis thaliana, the shoot and root apical meristems (SAM and RAM) regulate vertical growth and lateral growth. Meristems contain stem cells that differentiate to form organs under the influence of hormones and transcription factors. This thesis focuses on the ESR gene family: a subclass of the AP2/ERF super family of transcription factors. The ESR gene family has 6 members: ESR1/DRN, ESR2/DRNL, PUCHI, LEP, LEP2 (AT1G28160), and ESR3 (AT1G12890). Previous studies show that the ESR gene family plays a role in embryogenesis and floral/lateral root organogenesis, though the particular roles of LEP2 and ESR3 have not been defined. To further determine the “collective function” of the ESR gene family, I have generated ESR-gene-free plants named “esr sextuple (6x) mutants” using CRISPR/Cas9-mediated gene editing and selective mutant crossing over multiple generations. The lack of ESR genes led to incomplete flowers, though esr sextuple mutants retain the ability to transition into the reproductive phase. The esr sextuple (6x) mutants produced pin-like structures, indicating floral meristem arrest. The majority of esr sextuple mutants die right after gemination and most seedlings had no cotyledons. Preliminary auxin root elongation assays were conducted with a population of plants that were esr2 heterozygous and homozygous for the other ESR genes. I observed that the esr high-order mutants had delayed initiation of lateral root growth, similar to puchi single mutants. Transgenic lines overexpressing ESR3 and LEP2 were generated to further study their functions. Overexpression of ESR3 led to stunted growth, increased organ density along the stem, and rippled leaf phenotypes. Overexpression of LEP2 caused seed arrest, with few germinated seeds that died soon after germination.