A Novel RNA-Recognition-Motif Protein Is Required for Premeiotic G1/S-Phase Transition in Rice (Oryza sativa L.)

Abstract

The molecular mechanism for meiotic entry remains largely elusive in flowering plants. Only Arabidopsis SWI1/DYAD and maize AM1, both of which are the coiled-coil protein, are known to be required for the initiation of plant meiosis. The mechanism underlying the synchrony of male meiosis, characteristic to flowering plants, has also been unclear in the plant kingdom. In other eukaryotes, RNA-recognition-motif (RRM) proteins are known to play essential roles in germ-cell development and meiosis progression. Rice MEL2 protein discovered in this study shows partial similarity with human proline-rich RRM protein, deleted in Azoospermia-Associated Protein1 (DAZAP1), though MEL2 also possesses ankyrin repeats and a RING finger motif. Expression analyses of several cell-cycle markers revealed that, in mel2 mutant anthers, most germ cells failed to enter premeiotic S-phase and meiosis, and a part escaped from the defect and underwent meiosis with a significant delay or continued mitotic cycles. Immunofluorescent detection revealed that T7 peptide-tagged MEL2 localized at cytoplasmic perinuclear region of germ cells during premeiotic interphase in transgenic rice plants. This study is the first report of the plant RRM protein, which is required for regulating the premeiotic G1/S-phase transition of male and female germ cells and also establishing synchrony of male meiosis. This study will contribute to elucidation of similarities and diversities in reproduction system between plants and other species.

MEIOTIC F-BOX Is Essential for Male Meiotic DNA Double-Strand Break Repair in Rice

“…However, recent studies on meiosis arrested at leptotene (mel2) and ameiotic1 (am1) mutants suggest the existence of a meiotic leptotene/zygotene checkpoint in plants (Nonomura et al, 2011). The MEL2 gene encodes an RNA recognition motif-containing protein.…”

“…In the rice mel2 mutant, male meiocytes and tapetal cells were hypervacuolated and degenerated due to apoptosis. The mutation disturbed 80% of germ cells progressing into premeiotic S-phase and the remaining 20% into late zygotene (Nonomura et al, 2011). AM1 homologs encode a plant-specific protein with a coiled-coil domain.…”

COLLAPSED ABNORMAL POLLEN1Gene Encoding the Arabinokinase-Like Protein Is Involved in Pollen Development in Rice

“…The meiotic proteins MEIOSIS ARRESTED AT LEPTOTENE1 (MEL1), of the ARGONAUTE family of RNA interference (RNAi) proteins, HOMOLOGOUS PAIRING ABERRATION IN RICE MEIOSIS1-3, associated with synapsis of homologous chromosomes, and MEL2, a novel RNA recognition motif protein, are essential for viable pollen production (Nonomura et al, 2004a(Nonomura et al, , 2004b(Nonomura et al, , 2007(Nonomura et al, , 2011Yuan et al, 2009). The innermost layer (tapetum) of the anther wall is also important for early pollen stages, such as microsporocytes and microspores.…”

Genetic analysis and fine-mapping of a new rice mutant, white and lesion mimic leaf1

“…c Relative expression of genes associated with disease resistance and ROS between wild-type TN1 and wlml1 mutant plants reduced chlorophyll content during the early stages of plant development (Toda et al 2012). AM1 encodes a putative potassium efflux antiporter, and the am1 mutant exhibited a green/white variegation phenotype in the first few leaves, followed by an albino midrib phenotype in older tissues (Sheng et al 2014;Nonomura et al 2011). OsKS2 encodes a functional ent-beyerene synthase that is responsible for the biosynthesis of various diterpenoids (Tezuka et al 2015), and the mutant has short, dark green leaves (Ji et al 2014).…”