An insertional mutation in the rice PAIR2 gene, the ortholog of Arabidopsis ASY1, results in a defect in homologous chromosome pairing during meiosis

Abstract

To elucidate the genetic system that establishes homologous chromosome pairing in monocot plants, we have isolated an asynaptic mutant of rice, designated pair2 (homologous pairing aberration in rice meiosis 2), in which 24 completely unpaired univalents are observed at pachytene and diakinesis. The mutation was caused by an insertion of the retrotransposon Tos17, as demonstrated by complementation of the mutation by transformation with the corresponding wild-type gene. The gene in which the element was inserted is orthologous to the ASY1 gene of Arabidopsis thaliana and the HOP1 gene of Saccharomyces cerevisiae. Mature PAIR2 mRNA and several splicing variants were found to be highly expressed in wild-type reproductive tissues, and lower expression was also detected in vegetative tissues. In situ hybridization and BrdU incorporation experiments revealed that PAIR2 expression is specifically enhanced in male and female meiocytes, but not in those at pre-meiotic S phase or in the pollen maturation stages. The results obtained in this study suggest that the PAIR2 gene is essential for homologous chromosome pairing in meiosis, as in the case of the genes ASY1 and HOP1. The study also suggested the possibility that a highly homologous copy of the PAIR2 gene located on a different chromosome is in fact a pseudogene.

OsAM1 is required for leptotene-zygotene transition in rice

“…Compared with yeast, Arabidopsis and maize, the study of rice meiotic networks has lagged behind [26], and only a few genes have been identified [27][28][29][30][31][32][33]. Among them is a recently cloned gene MEL1 (MEIOSIS ARRESTED AT LEPTOTENE 1), which controls the progression of meiosis.…”

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

“…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].…”

“…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]. A mutation in PAIR2, the rice homolog of ASY1, causes defects in homolog alignment at pachytene and the formation of univalents instead of bivalents at diakinesis [63]. The PAIR2 proteins associate with axial elements (AEs) at leptotene and zygotene, and are removed from the AEs of arm regions when homologous chromosomes are synapsed [43].…”

“…A mutation in PAIR2, the rice homolog of ASY1, causes defects in homolog alignment at pachytene and the formation of univalents instead of bivalents at diakinesis [63]. The PAIR2 proteins associate with axial elements (AEs) at leptotene and zygotene, and are removed from the AEs of arm regions when homologous chromosomes are synapsed [43]. The Arabidopsis dmc1 mutant forms univalents instead of bivalents at meiotic prophase I and the recombination frequency is greatly reduced [59].…”

“…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.…”