Abstract
Cell number is a critical factor that determines kernel size in maize (Zea mays). Rapid mitotic divisions in early endosperm development produce most of the cells that make up the starchy endosperm; however, the mechanisms underlying early endosperm development remain largely unknown. We isolated a maize mutant that shows a varied-kernel-size phenotype (vks1). Vks1 encodes ZmKIN11, which belongs to the kinesin-14 subfamily and is predominantly expressed in early endosperm development. VKS1 dynamically localizes to the nucleus and microtubules and plays key roles in the migration of free nuclei in the coenocyte as well as in mitosis and cytokinesis in early mitotic divisions. Absence of VKS1 has relatively minor effects on plants but causes deformities in spindle assembly, sister chromatid separation, and phragmoplast formation in early endosperm development, thereby resulting in reduced cell proliferation. Severities of aberrant mitosis and cytokinesis within individual vks1 endosperms differ, thereby resulting in varied kernel sizes. Our discovery highlights VKS1 as a central regulator of mitosis in early maize endosperm development and provides a potential approach for future yield improvement.
Highlights
Flowering plants have evolved an advanced mode of reproduction known as double fertilization
When calculating the frequency of abnormal nuclei in the wild type and vks1, the nuclei in wild-type endosperm cells were almost normal, whereas the ratios of abnormal nuclei in vks1 ranged from 2.5 to 34.4% (Figure 7F). These results demonstrate that VKS1 is essential for mitosis and cytokinesis in early endosperm development
Considerable progress has been made understanding endosperm cell expansion associated with storage reserve synthesis and accumulation, far less is known about the genes that regulate cell number during early endosperm development
Summary
Flowering plants have evolved an advanced mode of reproduction known as double fertilization. KINDR can move neocentromeres along spindles to create meiotic drive, leading chromosomes to be preferentially transmitted to egg cells (Dawe et al, 2018) This finding explained the longstanding mystery of the meiotic drive of Ab10 (Schroeder and Malik, 2018). Another classic kinesin-14 member in maize is Divergent Spindle-1 (DV1), which is known to function in meiotic spindle pole organization (Higgins et al, 2016). The plant kinesin-14 subfamily contains many members (Vale and Goldstein, 1990), most of their molecular functions and biological roles in development remain to be elucidated. Mutation of vks results in defects in nuclear division and cytokinesis in early endosperm development and, as a consequence, leads to varied and small kernel sizes at seed maturity
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