The dicer-like1 Homolog fuzzy tassel Is Required for the Regulation of Meristem Determinacy in the Inflorescence and Vegetative Growth in Maize

Abstract

Plant architecture is determined by meristems that initiate leaves during vegetative development and flowers during reproductive development. Maize (Zea mays) inflorescences are patterned by a series of branching events, culminating in floral meristems that produce sexual organs. The maize fuzzy tassel (fzt) mutant has striking inflorescence defects with indeterminate meristems, fasciation, and alterations in sex determination. fzt plants have dramatically reduced plant height and shorter, narrower leaves with leaf polarity and phase change defects. We positionally cloned fzt and discovered that it contains a mutation in a dicer-like1 homolog, a key enzyme required for microRNA (miRNA) biogenesis. miRNAs are small noncoding RNAs that reduce target mRNA levels and are key regulators of plant development and physiology. Small RNA sequencing analysis showed that most miRNAs are moderately reduced in fzt plants and a few miRNAs are dramatically reduced. Some aspects of the fzt phenotype can be explained by reduced levels of known miRNAs, including miRNAs that influence meristem determinacy, phase change, and leaf polarity. miRNAs responsible for other aspects of the fzt phenotype are unknown and likely to be those miRNAs most severely reduced in fzt mutants. The fzt mutation provides a tool to link specific miRNAs and targets to discrete phenotypes and developmental roles.

The expanding world of small RNAs in plants

“…DCL1 knockdown in rice also results in defects in plant growth and in shoot, root, and leaf development, and ultimately leads to developmental arrest 11 . fuzzy tassel (fzt) mutants in maize have a broad range of vegetative and reproductive defects, and are hypomorphic dcl1 alleles, as in these plants the abundance of some miRNAs is more dramatically reduced than others 12 . The vast majority of MIRNA genes are species- or family-specific, suggesting rapid evolution and a high turnover rate 13,14 .…”

The Maize MID-COMPLEMENTING ACTIVITY Homolog CELL NUMBER REGULATOR13/NARROW ODD DWARF Coordinates Organ Growth and Tissue Patterning

“…Scanning electron microscopy was performed as described before (Thompson et al, 2014). Blades of adult, mature leaves were stained to detect hydrogen peroxide or superoxide ROS (Kumar et al, 2014).…”

Novel DICER-LIKE1 siRNAs Bypass the Requirement for DICER-LIKE4 in Maize Development

“…However, in contrast to mutants defective for ta-siRNA biogenesis, dcl1-2 leaves curl upward and are partially adaxialized with adaxial leaf characters, including the ligule, macrohairs, and bulliform cells, present also on the abaxial side (Supplemental Figures 7E to 7K). In addition, dcl1-2 plants show defects in inflorescence development reminiscent of the recently described dcl1-fzt mutant and are both male and female sterile (Supplemental Figures 7C and 7D; Thompson et al, 2014). Importantly, small RNA gel blot analysis shows that levels of miR166 and miR319 are reduced in dcl1-2 shoot apices relative to their wild-type siblings ( Figure 3C), providing evidence that the Mu insertion negatively impacts DCL1 activity.…”