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SUMMARY: Heat is a critical environmental stress for plant survival. One of its harmful effects on the cells is the disruption of genome integrity. However, the mechanisms by which plants cope with heat‐induced DNA damage remain largely unknown. RMI1, a component of the RTR (RECQ4‐TOP3α‐RMI1) complex, plays a pivotal role in maintaining genome stability. In this study, we identified the target gene RMI1 by characterizing a high‐temperature‐sensitive mutant. The growth and development of rmi1‐1 seedlings carrying a non‐frameshift mutation in RMI1 were hindered at 38°C. Abnormal mitotic chromosome behaviours ultimately led to the cell death of root tips. Additionally, the presence of chromosome fragments during anaphase I caused pollen abortion and sterility in rmi1‐1 plants. Yeast two‐hybrid assays revealed that the interactions between RMI1‐1 and RECQ4 or TOP3α were weakened with increasing temperature and entirely ceased at 36°C. In contrast, the functional RMI1 maintained its interactions with RECQ4 or TOP3α under the same conditions. These results indicate that the non‐frameshift mutation in RMI1 disrupts the formation of the RTR complex at high temperatures, leading to defects in DNA repair and increased sensitivity of rmi1‐1 under heat stress. However, embryos of the rmi1‐cr2 mutant with a frameshift mutation in RMI1 exhibited complete lethality. In addition, the overexpression of RMI1 enhanced the heat tolerance in rice. These findings provide insights into the molecular mechanisms that RMI1 responds to high temperatures by maintaining genome stability in rice. Significance Statement: RMI1 is essential for rice growth and development at high temperature. [ABSTRACT FROM AUTHOR]

SUMMARY: The pairing and synapsis of homologous chromosomes are crucial for their correct segregation during meiosis. The LINC (Linker of Nucleoskeleton and Cytoskeleton) complex can recruit kinesin protein at the nuclear envelope, affecting telomere bouquet formation and homologous pairing. Kinesin‐1‐like protein Pollen Semi‐Sterility1 (PSS1) plays a pivotal role in male meiotic chromosomal behavior and is essential for fertility in rice. However, its exact role in meiosis, especially as kinesin involved in homologous pairing and synapsis, has not been fully elucidated. Here, we generated three pss1 mutants by genome editing technology to dissect PSS1 biological functions in meiosis. The pss1 mutants exhibit alterations in the radial microtubule organization at pachytene and manifest a deficiency in telomere clustering, which is critical for full‐length homologous pairing. We reveal that PSS1 serves as a key mediator between chromosomes and cytoskeleton, thereby regulating microtubule organization and transmitting the force to nuclei to facilitate homologous chromosome pairing and synapsis in meiosis. Significance Statement: The source of energy driving the rapid movement of chromosomes during prophase I in rice meiosis remains to be elucidated In this manuscript, we speculate a novel mechanism that PSS1 serves as a crucial mediator between chromosomes and skeleton, thereby regulating microtubule organization and transmitting the force to nuclei to facilitating homologous chromosome pairing and synapsis in meiosis. [ABSTRACT FROM AUTHOR]

Summary: Fluorescence in situ hybridization using probes based on oligonucleotides (oligo‐FISH) is a useful tool for chromosome identification and karyotype analysis. Here we developed two oligo‐FISH probes that allow the identification of each of the 12 pairs of chromosomes in rice (Oryza sativa). These two probes comprised 25 717 (green) and 25 215 (red) oligos (45 nucleotides), respectively, and generated 26 distinct FISH signals that can be used as a barcode to uniquely label each of the 12 pairs of rice chromosomes. Standard karyotypes of rice were established using this system on both mitotic and meiotic chromosomes. Moreover, dual‐color oligo‐FISH was used to characterize diverse chromosomal abnormalities. Oligo‐FISH analyses using these probes in various wild Oryza species revealed that chromosomes from the AA, BB or CC genomes generated specific and intense signals similar to those in rice, while chromosomes with the EE genome generated less specific signals and the FF genome gave no signal. Together, the oligo‐FISH probes we established will be a powerful tool for studying chromosome variations and evolution in the genus Oryza. Significance Statement: Dual‐color oligo‐FISH was established to allow identification of the 12 chromosomes in mitosis and meiosis of rice, which will be a useful tool for studying chromosome variations and evolution in the Oryza genus. [ABSTRACT FROM AUTHOR]

We previously isolated a complete set of primary trisomics along with many other aneuploids from triploid plants derived from an indica rice variety 'Zhongxian 3037.' About 30,000 progeny from these trisomic and aneuploid plants were grown each year from 1994 to 1999. The variants that differed morphologically from both the diploids and the original primary trisomics were collected for cytological identification. From these variants, a complete set of telotrisomics covering all 24 rice chromosome arms was obtained. The identities of the extra chromosomes were further confirmed by dosage analysis of the RFLP markers on extra chromosome arms. The telocentric nature of the extra chromosomes in these stocks was verified by fluorescence in situ hybridization (FISH) using a rice centromeric BAC clone as a marker probe. In general, the shorter the extra chromosome arm of a telotrisomic, the stronger the resemblance it bears to the diploid; the longer the extra chromosome arm, the stronger the resemblance to the corresponding primary trisomic. We demonstrated that DNA clones can be rapidly assigned to specific chromosome arms by dosage analysis with the telotrisomics. We also showed that telotrisomics are valuable tools tot chromosome microdissection and for developing chromosome-specific DNA markers.