Summary: Meiosis is essential for eukaryotic sexual reproduction, with two consecutive rounds of nuclear divisions, allowing production of haploid gametes. Information regarding the meiotic transcriptome should provide valuable clues about global expression patterns and detailed gene activities. Here we used RNA sequencing to explore the transcriptome of a single plant cell type, the Arabidopsis male meiocyte, detecting the expression of approximately 20 000 genes. Transcription of introns of >400 genes was observed, suggesting previously unannotated exons. More than 800 genes may be preferentially expressed in meiocytes, including known meiotic genes. Of the 3378 Pfam gene families in the Arabidopsis genome, 3265 matched meiocyte‐expressed genes, and 18 gene families were over‐represented in male meiocytes, including transcription factor and other regulatory gene families. Expression was detected for many genes thought to encode meiosis‐related proteins, including MutS homologs (MSHs), kinesins and ATPases. We identified more than 1000 orthologous gene clusters that are also expressed in meiotic cells of mouse and fission yeast, including 503 single‐copy genes across the three organisms, with a greater number of gene clusters shared between Arabidopsis and mouse than either share with yeast. Interestingly, approximately 5% transposable element genes were apparently transcribed in male meiocytes, with a positive correlation to the transcription of neighboring genes. In summary, our RNA‐Seq transcriptome data provide an overview of gene expression in male meiocytes and invaluable information for future functional studies.

During angiosperm microsporogenesis, callose serves as a temporary wall to separate microsporocytes and newly formed microspores in the tetrad. Abnormal callose deposition and dissolution can lead to degeneration of developing microspores. However, genes and their regulation in callose metabolism during microsporogenesis still remain largely unclear. Here, we demonstrated that the Arabidopsis (Arabidopsis thaliana) CALLOSE DEFECTIVE MICROSPORE1 (CDM1) gene, encoding a tandem CCCH-type zinc finger protein, plays an important role in regulation of callose metabolism in male meiocytes and in integrity of newly formed microspores. First, quantitative reverse transcription PCR and in situ hybridization analyses showed that the CDM1 gene was highly expressed in meiocytes and the tapetum from anther stages 4 to 7. In addition, a transfer DNA insertional cdm1 mutant was completely male sterile. Moreover, light microscopy of anther sections revealed that microspores in the mutant anther were initiated, and then degenerated soon afterward with callose deposition defects, eventually leading to male sterility. Furthermore, transmission electron microscopy demonstrated that pollen exine formation was severely affected in the cdm1 mutant. Finally, we found that the cdm1 mutation affected the expression of callose synthesis genes (CALLOSE SYNTHASE5 and CALLOSE SYNTHASE12) and potential callase-related genes (A6 and MYB80), as well as three other putative β-1,3-glucanase genes. Therefore, we propose that the CDM1 gene regulates callose metabolism during microsporogenesis, thereby promoting Arabidopsis male fertility.

Summary: Anther development, particularly around the time of meiosis, is extremely crucial for plant sexual reproduction. Meanwhile, cell‐to‐cell communication between somatic (especial tapetum) cells and meiocytes are important for both somatic anther development and meiosis. To investigate possible molecular mechanisms modulating protein activities during anther development, we applied high‐resolution mass spectrometry‐based proteomic and phosphoproteomic analyses for developing rice (Oryza sativa) anthers around the time of meiosis (RAM). In total, we identified 4984 proteins and 3203 phosphoproteins with 8973 unique phosphorylation sites (p‐sites). Among those detected here, 1544 phosphoproteins are currently absent in the Plant Protein Phosphorylation DataBase (P³DB), substantially enriching plant phosphorylation information. Mapman enrichment analysis showed that ‘DNA repair’,’transcription regulation’ and ‘signaling’ related proteins were overrepresented in the phosphorylated proteins. Ten genetically identified rice meiotic proteins were detected to be phosphorylated at a total of 25 p‐sites; moreover more than 400 meiotically expressed proteins were revealed to be phosphorylated and their phosphorylation sites were precisely assigned. 163 putative secretory proteins, possibly functioning in cell‐to‐cell communication, are also phosphorylated. Furthermore, we showed that DNA synthesis, RNA splicing and RNA‐directed DNA methylation pathways are extensively affected by phosphorylation. In addition, our data support 46 kinase‐substrate pairs predicted by the rice Kinase‐Protein Interaction Map, with SnRK1 substrates highly enriched. Taken together, our data revealed extensive protein phosphorylation during anther development, suggesting an important post‐translational modification affecting protein activity.

The plant-specific F-box protein MEIOTIC F-BOX plays critical roles in male meiotic DNA double-strand break repair and is required for male meiotic progression

The phytohormone ethylene plays a crucial role in the production and accumulation of reactive oxygen species (ROS) in plants under stress conditions. Ethylene response factors (ERFs) are important ethylene-signaling regulators functioning in plant defense responses against biotic and abiotic stresses. However, the roles of ERFs during plant adapting to ROS stress have not yet been well documented. Our studies previously reported that a tomato ERF transcription factor TERF1 functions in the regulation of plant ethylene responses and stress tolerance. Here, we report our findings regarding the roles of TERF1 in ROS scavenging. In this study, we revealed that the transcription of TERF1 is regulated by upstream EIN3-like (EIN3, ethylene-insensitive 3) regulators LeEIL3 and LeEIL4 in tomato (Solanum lycopersicum) and is also inducible by exogenous applied ROS-generating reagents. Ectopic expression of TERF1 in tobacco promoted the expression of genes involved in oxidative stress responses, including carbonic anhydrase functioning in hypersensitive defense, catalase and glutathione peroxidase catalyzing oxidative reactions and GDP-D-mannose pyrophosphorylase functioning in ascorbic acid biosynthesis, reduced the ROS content induced by ethylene treatment and enhanced stress tolerance of tobacco seedlings to hydrogen peroxide (H₂O₂). Cumulatively, these findings suggest that TERF1 is an ethylene inducible factor regulating ROS scavenging during stress responses.