Mapping and characterization of the tls4 mutant in maize reveals potential role for endocytosis in auxin related tassel development

Characterizing the genes involved in regulating the reproductive development of corn is important for maximizing crop yields. For example, breeding crops that do not need to be de-tasseled would allow for more effective production of hybrid corn, which grows sturdier and larger plants resulting in higher yields. The tassel-less4 (tls4) mutant in Zea mays (maize), generated by ethyl methane sulfonate (EMS) mutagenesis, exhibits defective reproductive development of the male inflorescence (tassel), and has vegetative defects including reduced height and narrow leaves. In this study, I sought to identify the tls4 gene and characterize its functions, in order to shed light onto the specific mechanisms of inflorescence development while also revealing a potential regulatory link between vegetative and reproductive development. Previous mapping of the causative gene revealed tls4 to be located within bin 4.10 on chromosome 4. Discrepancies between mapping strategies were examined for signs of co-segregating DNA from a different genetic background. Molecular markers were used to further map the location of tls4 within the genome. The mapped target region identified was 650kbp, contained 32 genes, and had an EMS signature mutation within EHD1. The EHD1 protein is involved in endocytosis, suggesting the tls4 phenotype may result from a defect in endocytosis. To test this hypothesis, I conducted an endocytosis assay that revealed potential endocytosis defects in tls4, further supporting EHD1 as the candidate tls4 gene. The phenotypic traits of tls4 are characteristic of defects related to the plant growth hormone auxin, which regulates organogenesis through a large genetic network. To investigate a possible role for tls4 within this genetic network, I carried out a double mutant analysis between tls4 and an auxin transport mutant, barren inflorescence2 (bif2), which revealed a synergistic interaction in tassels. This work identifies a promising candidate gene for tls4 and a potential role for endocytosis in regulating auxin-related reproductive development of maize. Though additional studies are warranted, these data expand our understanding of the auxin genetic network and aid the work to maximize crop production by developing maize crops with modified tassels.