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

Nonsense-mediated RNA decay (NMD) is an RNA control mechanism that has also been implicated in the broader regulation of gene expression. Nevertheless, a role for NMD in genome regulation has not yet been fully assessed, partially because NMD inactivation is lethal in many organisms. Here, we performed an in-depth comparative analysis of Arabidopsis (Arabidopsis thaliana) mutants lacking the NMD-related proteins UPF3, UPF1, and SMG7. We found different impacts of these proteins on NMD and the Arabidopsis transcriptome, with UPF1 having the biggest effect. Transcriptome assembly in UPF1-null plants revealed genome-wide changes in alternative splicing, suggesting that UPF1 functions in splicing. The inactivation of UPF1 led to translational repression, as manifested by a global shift in mRNAs from polysomes to monosomes and the downregulation of genes involved in translation and ribosome biogenesis. Despite these global changes, NMD targets and mRNAs expressed at low levels with short half-lives were enriched in the polysomes of upf1 mutants, indicating that UPF1/NMD suppresses the translation of aberrant RNAs. Particularly striking was an increase in the translation of TIR domain-containing, nucleotide binding, leucine-rich repeat (TNL) immune receptors. The regulation of TNLs via UPF1/NMD-mediated mRNA stability and translational derepression offers a dynamic mechanism for the rapid activation of TNLs in response to pathogen attack.

• MeSH
• Alternative Splicing MeSH
• Arabidopsis genetics   metabolism   MeSH
• Mutation MeSH
• Nonsense Mediated mRNA Decay * MeSH
• Protein Processing, Post-Translational MeSH
• Arabidopsis Proteins genetics   metabolism   MeSH
• Protein Biosynthesis MeSH
• Gene Expression Regulation, Plant MeSH
• RNA Helicases genetics   metabolism   MeSH
• Carrier Proteins genetics   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Arabidopsis Proteins MeSH
• RNA Helicases MeSH
• RPS6 protein, Arabidopsis MeSH Browser
• SMG7 protein, Arabidopsis MeSH Browser
• Carrier Proteins MeSH
• UPF1 protein, Arabidopsis MeSH Browser
• UPF3 protein, Arabidopsis MeSH Browser

In higher plants, germline differentiation occurs during a relatively short period within developing flowers. Understanding of the mechanisms that govern germline differentiation lags behind other plant developmental processes. This is largely because the germline is restricted to relatively few cells buried deep within floral tissues, which makes them difficult to study. To overcome this limitation, we have developed a methodology for live imaging of the germ cell lineage within floral organs of Arabidopsis using light sheet fluorescence microscopy. We have established reporter lines, cultivation conditions, and imaging protocols for high-resolution microscopy of developing flowers continuously for up to several days. We used multiview imagining to reconstruct a three-dimensional model of a flower at subcellular resolution. We demonstrate the power of this approach by capturing male and female meiosis, asymmetric pollen division, movement of meiotic chromosomes, and unusual restitution mitosis in tapetum cells. This method will enable new avenues of research into plant sexual reproduction.

• Keywords
• A. thaliana, SPIM, cell biology, flower, germline, light sheet microscopy, live cell imaging, meiosis, plant biology,
• MeSH
• Arabidopsis cytology   growth & development   MeSH
• Cell Differentiation * MeSH
• Cytogenetic Analysis MeSH
• Flowers cytology   growth & development   MeSH
• Microscopy methods   MeSH
• Germ Cells, Plant cytology   MeSH
• Publication type
• Journal Article MeSH
• Evaluation Study MeSH
• Research Support, Non-U.S. Gov't MeSH