Meiosis is a specialized cell division that halves the number of chromosomes in two consecutive rounds of chromosome segregation. In angiosperm plants is meiosis followed by mitotic divisions to form rudimentary haploid gametophytes. In Arabidopsis, termination of meiosis and transition to gametophytic development are governed by TDM1 and SMG7 that mediate inhibition of translation. Mutants deficient in this mechanism do not form tetrads but instead undergo multiple cycles of aberrant nuclear divisions that are likely caused by the failure to downregulate cyclin dependent kinases during meiotic exit. A suppressor screen to identify genes that contribute to meiotic exit uncovered a mutation in cyclin-dependent kinase D;3 (CDKD;3) that alleviates meiotic defects in smg7 deficient plants. The CDKD;3 deficiency prevents aberrant meiotic divisions observed in smg7 mutants or delays their onset after initiation of cytokinesis, which permits formation of functional microspores. Although CDKD;3 acts as an activator of cyclin-dependent kinase A;1 (CDKA;1), the main cyclin dependent kinase that regulates meiosis, cdkd;3 mutation appears to promote meiotic exit independently of CDKA;1. Furthermore, analysis of CDKD;3 interactome revealed enrichment for proteins implicated in cytokinesis, suggesting a more complex function of CDKD;3 in cell cycle regulation.

• Keywords
• Arabidopsis thaliana, cell cycle, cyclin dependent kinase, cytokinesis, meiosis,
• Publication type
• Journal Article MeSH

Meiosis in angiosperm plants is followed by mitotic divisions to form multicellular haploid gametophytes. Termination of meiosis and transition to gametophytic development is, in Arabidopsis, governed by a dedicated mechanism that involves SMG7 and TDM1 proteins. Mutants carrying the smg7-6 allele are semi-fertile due to reduced pollen production. We found that instead of forming tetrads, smg7-6 pollen mother cells undergo multiple rounds of chromosome condensation and spindle assembly at the end of meiosis, resembling aberrant attempts to undergo additional meiotic divisions. A suppressor screen uncovered a mutation in centromeric histone H3 (CENH3) that increased fertility and promoted meiotic exit in smg7-6 plants. The mutation led to inefficient splicing of the CENH3 mRNA and a substantial decrease of CENH3, resulting in smaller centromeres. The reduced level of CENH3 delayed formation of the mitotic spindle but did not have an apparent effect on plant growth and development. We suggest that impaired spindle re-assembly at the end of meiosis limits aberrant divisions in smg7-6 plants and promotes formation of tetrads and viable pollen. Furthermore, the mutant with reduced level of CENH3 was very inefficient haploid inducer indicating that differences in centromere size is not the key determinant of centromere-mediated genome elimination.

• MeSH
• Spindle Apparatus MeSH
• Arabidopsis genetics   physiology   MeSH
• Fertility genetics   MeSH
• Meiosis genetics   MeSH
• RNA, Messenger genetics   MeSH
• Mutation * MeSH
• Arabidopsis Proteins genetics   MeSH
• Genes, Plant * MeSH
• Carrier Proteins genetics   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• RNA, Messenger MeSH
• Arabidopsis Proteins MeSH
• SMG7 protein, Arabidopsis MeSH Browser
• Carrier Proteins MeSH

Cell polarity is a fundamental feature of all multicellular organisms. PIN auxin transporters are important cell polarity markers that play crucial roles in a plethora of developmental processes in plants. Here, to identify components involved in cell polarity establishment and maintenance in plants, we performed a forward genetic screening of PIN2:PIN1-HA;pin2 Arabidopsis (Arabidopsis thaliana) plants, which ectopically express predominantly basally localized PIN1 in root epidermal cells, leading to agravitropic root growth. We identified the regulator of PIN polarity 12 (repp12) mutation, which restored gravitropic root growth and caused a switch in PIN1-HA polarity from the basal to apical side of root epidermal cells. Next Generation Sequencing and complementation experiments established the causative mutation of repp12 as a single amino acid exchange in Aminophospholipid ATPase3 (ALA3), a phospholipid flippase predicted to function in vesicle formation. repp12 and ala3 T-DNA mutants show defects in many auxin-regulated processes, asymmetric auxin distribution, and PIN trafficking. Analysis of quintuple and sextuple mutants confirmed the crucial roles of ALA proteins in regulating plant development as well as PIN trafficking and polarity. Genetic and physical interaction studies revealed that ALA3 functions together with the ADP ribosylation factor GTPase exchange factors GNOM and BIG3 in regulating PIN polarity, trafficking, and auxin-mediated development.

• MeSH
• ADP-Ribosylation Factors metabolism   MeSH
• Arabidopsis drug effects   metabolism   MeSH
• Biological Transport drug effects   MeSH
• Brefeldin A pharmacology   MeSH
• Cell Membrane drug effects   metabolism   MeSH
• Epistasis, Genetic drug effects   MeSH
• GTP Phosphohydrolases metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Mutation genetics   MeSH
• Arabidopsis Proteins metabolism   MeSH
• Phospholipid Transfer Proteins metabolism   MeSH
• Nicotiana metabolism   MeSH
• trans-Golgi Network drug effects   metabolism   MeSH
• Protein Binding drug effects   MeSH
• Guanine Nucleotide Exchange Factors metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• ADP-Ribosylation Factors MeSH
• Brefeldin A MeSH
• GTP Phosphohydrolases MeSH
• Indoleacetic Acids MeSH
• Arabidopsis Proteins MeSH
• Phospholipid Transfer Proteins MeSH
• Guanine Nucleotide Exchange Factors MeSH