Characterizing the vegetative phenotype of fzt maize mutant

Abstract

microRNAs are short, non-coding RNA strands that regulate gene expression post-transcriptionally in all multicellular organisms. miRNAs begin as a hairpin in the nucleus. The primary miRNA (pri-miRNA) and preliminary miRNA (pre-miRNA) are cleaved by DICER-LIKE1 to form the miRNA, demonstrating this protein is essential for the proper biogenesis of miRNAs. Once the miRNA is formed, it regulates gene expression by mRNA cleavage or translation repression. fzt is a maize mutant with a missense mutation in DICER-LIKE1. The fzt mutant has abnormal vegetative and reproductive tissue phenotypes. My research focuses on the vegetative development of the mutant. The mutant plants are shorter in stature with shorter and narrower leaves compared to their normal siblings. miRNAs have well established roles in plant development, including establishing leaf polarity and phase change. A complex mechanism involving specific miRNAs establishes proper adaxial and abaxial leaf polarity, including miR390, miR165, and miR166. A balance of two known miRNAs promotes juvenile and adult characteristics; miR156 and miR172. Both of these developmental functions were analyzed in this project. We also investigated the difference in leaf size between the normal sibling and mutant plants by looking at cell size, cell number, and cell proliferation. We found a difference in both the leaf polarity and phase change between the normal sibling and fzt mutant. Epidermal cell types in maize are surface-specific. We found an adaxialization of the abaxial surface, as well as an abaxialization of the adaxial surface by scanning electron microscopy. This polarity defect was more severe in the Mo17-background mutant plants. We also found a subtle polarity defect in the vasculature of adult leaves in the Mo17-background. Phase change was analyzed using epidermal peels and Toluidine Blue O staining. In both the A619- and Mo17-backgrounds, we found an adult transition one-leaf early. The size difference of the normal sibling and mutant plants was examined by cell size measurements and cell counts using epidermal peels. Cell proliferation was analyzed by examining tubulin dynamics in the pre- and post-differentiation zones of adult maize leaves. Maize is an essential crop plant, and has recently been used to explore alternate fuel alternatves. Further understanding maize development could lead to an increase in yield, both ear and leaf tissue.