The semidominant mutation Liguleless3-O (Lg3-O) causes a blade-to-sheath transformation at the midrib region of the maize (Zea mays L.) leaf. We isolated a full-length lg3 cDNA containing a knotted1-like family homeobox. Six Lg3-O partial revertant alleles caused by insertion of a Mutator (Mu) transposon and two deletion derivatives were isolated and used to verify that our knotted1-like cDNA corresponds to the LG3 message. In wild-type plants the LG3 mRNA is expressed in apical regions but is not expressed in leaves. In mutant plants harboring any of three dominant lg3 alleles (Lg3-O, -Mlg, and -347), LG3 mRNA is expressed in leaf sheath tissue, indicating that the Lg3 phenotype is due to ectopic expression of the gene. The Lg3-O revertant alleles represent two classes of Lg3 phenotypes that correlate well with the level of ectopic Lg3 expression. High levels of ectopic LG3 mRNA expression results in a severe Lg3 phenotype, whereas weak ectopic Lg3 expression results in a mild Lg3 phenotype. We propose that ectopic Lg3 expression early in leaf development causes the blade-to-sheath transformation, but the level of expression determines the extent of the transformation.Maize (Zea mays L.) leaf development is thought to be divided into three distinct stages (Sylvester et al., 1990(Sylvester et al., , 1996. In the first stage the vegetative meristem recruites an overlapping ring of founder cells that will form the next phytomer: a repeating segment of the maize plant composed of the leaf, internode, node, and bud (Galinat, 1959). In the second stage, a subset of the founder cells, the leaf founder cells divide equally into an undifferentiated primordium. During the third stage, growth and differentiation of the primordium occur to form the mature leaf. Maize leaves are divided into three parts: the sheath, the ligular region, and the blade, as shown in Figure 1. The proximal sheath wraps around the culm and provides support for the plant. The distal blade grows out from the main axis of the plant and is its major photosynthetic organ. The ligular region, composed of the ligule and two wedgeshaped auricles, separates the sheath from the blade. Many mutations affect maize leaf development and in particular disrupt or displace the blade-sheath boundary and the associated ligule and auricle (Freeling and Hake, 1985; Becraft et al., 1990; Becraft and Freeling, 1994; Fowler and Freeling, 1996; Harper and Freeling, 1996; Schichnes and Freeling, 1998).The semidominant Liguleless3-O (Lg3-O) mutation results in a blade-to-sheath transformation at the midrib region of the maize leaf (Fig. 1B; Fowler and Freeling, 1996). Blade, auricle, and ligule regions are replaced by sheath at the midrib region, and at the midrib the ligule is removed. The blade-to-sheath transformation in the Lg3-O mutant causes the ligule to develop at the new blade-sheath boundary, distal to the location of wild-type ligules. The displaced ligule gradually approaches the wild-type position at the leaf margin ( Fig. 1B; Muehlbauer et al., 1997). Homo...

Ipl1/Aurora-mediated phosphorylation of the CPC component Sli15/INCENP promotes microtubule dynamics by restricting CPC–spindle association.

The Aurora kinase complex, also called the chromosomal passenger complex (CPC), is essential for faithful chromosome segregation and completion of cell division. In Fungi and Animalia, this complex consists of the kinase Aurora B/AIR-2/Ipl1p, INCENP/ICP-1/Sli15p, and Survivin/BIR-1/Bir1p. A fourth subunit, Borealin/Dasra/CSC-1, is required for CPC targeting to centromeres and central spindles and has only been found in Animalia. Here we identified a new core component of the CPC in budding yeast, Nbl1p. NBL1 is essential for viability and nbl1 mutations cause chromosome missegregation and lagging chromosomes. Nbl1p colocalizes and copurifies with the CPC, and it is essential for CPC localization, stability, integrity, and function. Nbl1p is related to the N-terminus of Borealin/Dasra/CSC-1 and is similarly involved in connecting the other CPC subunits. Distant homology searching identified nearly 200, mostly unannotated, Borealin/Dasra/CSC-1-related proteins from nearly 150 species within Fungi and Animalia. Analysis of the sequence of these proteins, combined with comparative protein structure modeling of Bir1p-Nbl1p-Sli15p using the crystal structure of the human Survivin-Borealin-INCENP complex, revealed a striking structural conservation across a broad range of species. Our biological and computational analyses therefore establish that the fundamental design of the CPC is conserved from Fungi to Animalia.

The nine class-I maize (Zea mays L.) knox genes are putative transcription factors normally expressed in shoot apices, but not in leaves. knotted1 (kn1) seems to function in shoot apical meristem maintenance, and rough sheath1 (rs1)-like genes may act in internode elongation. The function of liguleless3 (lg3)-type genes is still unknown. Here, we characterized lg3 as well as the two most closely related genes liguleless4a (lg4a, formerly knox11) and liguleless4b (lg4b, formerly knox5). We termed this subclass of knox genes lg3/4 genes. We studied the expression patterns of lg3/4 genes and compared their sequences. We obtained knockout mutants of lg3 by finding Mu transposon insertions into exons. Our results show that lg3 was not essential for plant development, and that lg4a and lg4b were likely to encode the redundant function. In addition, lg4a but not lg4b was ectopically expressed in the Lg4-O mutant, suggesting that this mutant was affected at the lg4a locus. We found that the lg3 gene was unique among knox genes as it was co-induced in the leaves of leaf mutants that ectopically expressed knox genes in the leaves. The leaf phenotype expressed in the dominant Rs1-O mutant was not altered when lg3 function was removed using the knockout. Genomic sequence comparisons of lg3, lg4a and lg4b from maize and the two homologous genes, osh6 and osh71, from rice revealed a 14-bp phylogenetic footprint in intron II. This sequence was conserved in nucleotide composition, position and polarity in the lg3/4 genes of divergent grasses representing six Gramineae subfamilies. In an independent experiment, this same conserved sequence was found in a yeast reverse one-hybrid screen for putative binding sites of the LG3 homeodomain protein. Distribution of this 14-bp sequence was examined within the public rice database. The possible function of this sequence in regulation of lg3/4 genes is discussed.

CK2 associates with kinetochore protein Mif2/CENP-C. Loss of CK2 results in defects in chromosome segregation, short mitotic spindle, and activation of the spindle assembly checkpoint. CK2 phosphorylates Mif2 and Ndc10. CK2 phosphorylation plays antagonistic and synergistic roles with Aurora B phosphorylation of Mif2 and Ndc10, respectively.