The Rice OsRad21-4, an Orthologue of Yeast Rec8 Protein, is Required for Efficient Meiosis

Abstract

In yeast, Rad21/Scc1 and its meiotic variant Rec8 are key players in the establishment and subsequent dissolution of sister chromatid cohesion for mitosis and meiosis, respectively, which are essential for chromosome segregation. Unlike yeast, our identification revealed that the rice genome has 4 RAD21-like genes that share lower than 21% identity at polypeptide levels, and each is present as a single copy in this genome. Here we describe our analysis of the function of OsRAD21-4 by RNAi. Western blot analyses indicated that the protein was most abundant in young flowers and less in leaves and buds but absent in roots. In flowers, the expression was further defined to premeiotic pollen mother cells (PMCs) and meiotic PMCs of anthers. Meiotic chromosome behaviors were monitored from male meiocytes of OsRAD21-4-deficient lines mediated by RNAi. The male meiocytes showed multiple aberrant events at meiotic prophase I, including over-condensation of chromosomes, precocious segregation of homologues and chromosome fragmentation. Fluorescence in situ hybridization experiments revealed that the deficient lines were defective in homologous pairing and cohesion at sister chromatid arms. These defects resulted in unequal chromosome segregation and aberrant spore generation. These observations suggest that OsRad21-4 is essential for efficient meiosis.

Functional conservation of the meiotic genes SDS and RCK in male meiosis in the monocot rice

“…The male meiocytes in OsRAD21-4-deficient lines showed overcondensation of chromosomes, precocious segregation of homologs and chromosome fragmentation. Fluorescence in situ hybridization revealed that OsRAD21-4-deficient lines were defective in homologous pairing and cohesion at sister chromatid arms [45]. These results strongly support a conserved molecular mechanism for male meiosis in monocots and eudicots.…”

“…In addition to the conserved sequences and functions of rice SDS and RCK shown in this study, a small number of rice meiosis genes have been studied including PAIR2 [43], OsDMC1 [44], OsRad21-4 [45] and their functions in rice male meiosis are conserved compared to their correspondent homologous genes ASY1 [58], AtDMC1 [59,60], SYN1 [61] in Arabidopsis. In Arabidopsis, the ASY1 protein is localized to the axial/lateral elements and an asy1 mutant is asynaptic and unable to form SC in both male and female meiocytes, indicating its critical role in SC formation [54,58,62].…”

“…Pollen grains emitting green fluorescence were regarded as viable pollen. Pollen number per flower was counted with a hematocyte arithmometer, and the data is estimated from 30 independent flowers for each line [45]. Chromosome spreading and 4,6-Diamidino-2-phenylindole (DAPI) staining were performed according to Ross et al [71] with some modifications.…”

“…The monocot rice is an excellent system for studying the molecular mechanism of meiosis [41]. In recent years, a few rice meiotic genes have been reported, including PAIR1 [42], PAIR2 [43], OsDMC1 [44], OsRad21-4 [45] and OsRad21-3 [46]. To investigate the functional evolution of SDS and RCK, we have identified the putative rice orthologs of SDS and RCK, and studied their functions using RNAi-mediated reverse genetic approaches.…”

OsAM1 is required for leptotene-zygotene transition in rice

“…Cohesin proteins, which are thought to be involved in this process, have been extensively studied in yeast and animals [4][5][6]. In plants, some cohesin proteins have been characterized for their influence in meiotic pairing, especially the REC8 homologs: SYN1/DIF1 in Arabidopsis [7][8][9], AFD1 in maize [10] and OsRAD21-4 in rice [11]. It is becoming evident that the cohesin complex provides the basis for AE assembly and is implicated in various meiotic events [4,12].…”