Os03g0650400

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Annotated Information

Function

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Mutation

• The mutant plant was normal in vegetative development, although no pollen was produced (Figure 1A and 1B). Normal phenotype plants and sterile plants from the progeny of Osam1 +/− give 3:1 segregation, establishing it as a single recessive mutant (χ2 = 0.83; P > 0.05). The researchers named the mutant Osam1-1. When pollinated with normal pollen from wild-type plants, Osam1-1 plants do not set seeds.

Figure 1 Comparison of the wild-type and Osam1-1 mutant phenotype. (A) A wild-type plant (left) and an Osam1-1 mutant plant (right). (B) A wild-type panicle (left) and an Osam1-1 mutant panicle (right). .

• To determine the anther morphological defects in Osam1- 1, transverse sections of both wild-type and mutant anthers at different developmental stages were examined. The development of rice anthers has been described in detail. Before entering meiosis, the four-layered anther wall, including epidermis, endothecium, middle layer and tapetum, is formed and primary sporogenous cells develop into larger PMCs in the anther locules (Figure 2A). The PMCs gradually become spherical and enter meiosis (Figure 2B and 2C). At the end of meiosis, the PMCs develop into tetrads. Concomitantly, the middle layer and tapetum begin to degenerate. After going through the vacuolated stage (Figure 2D) and two rounds of mitosis (Figure 2E), microspores then generate the mature tricellular pollen grains (Figure 2F). There was no detectable difference between Osam1-1 and wild-type anthers before entering meiosis, and the four layers of anther wall were also normal (Figure 2G). The impairment of anther development was observed in Osam1-1 after PMCs enlarged and entered meiosis (Figure 2H). The tapetal cells had significantly swelled and the PMCs did not complete meiosis (Figure 2I). The development of PMCs in Osam1-1 anthers seemed to be interrupted; they were arrested at the PMC stage with aberrant tapetum development (Figure 2J and 2K). Eventually, all the PMCs as well as tapetum had disappeared, leading to the anthers without pollen (Figure 2L).

Figure 2 Transverse sections of anthers in both wild type and the Osam1-1 mutant. As the development of the Osam1-1 PMCs was arrested, the sections of Osam1-1 anthers were selected according to the length of spikelet. The wild-type sections are shown in A-F, and the Osam1-1 sections are shown in G-L. (A, B, G, H) Early meiosis stage. (C, I) Late meiosis stage. (D, J) Vacuolated pollen stage. (E, K) Pollen mitosis stage. (F, L) Mature pollen stage. E, epidermis; En, endothecium; ML, middle layer; T, tapetum; PMCs, pollen mother cells; MP, mature pollen. Scale bars, 5 μm. .

• In wild-type PMCs, early leptotene chromosomes begin to condense and individual chromosomes appear as thin threads (Figure 3A), while nucleoli move to the periphery of the nuclei in late leptotene (Figure 3B). As zygotene progresses, homologous chromosomes undergo pairing and synapsis (Figure 3C). At pachytene, fully synapsed chromosomes are observed (Figure 3D). SCs are then disassembled, and chiasmata, which correspond to crossovers, hold the homologous chromosomes together at diplotene. During diakinesis, the chromosomes are highly condensed and 12 short bivalents are clearly observed (Figure 3E). At metaphase I, the bivalents become aligned in the center of the cell (Figure 3F), and then homologous chromosomes separate and migrate toward opposite poles at anaphase I (Figure 3G), generating dyads at the end of meiosis I. During meiosis II, the two dyads undergo equational division and produce tetrads (Figure 3H and 3I). The Osam1-1 chromosomes behaved normally during meiotic interphase and leptotene (Figure 4A and 4B). However, the later stages of prophase I were never observed; the meiotic process seemed to have been arrested at leptotene, although some chromosomes continue to condense (Figure 4C). The abnormal PMCs remained in leptotene for some time (Figure 4D). The researchers have checked more than 300 PMCs in the Osam1-1 mutant and all of them showed the same characteristics. They also found that Osam1-2 meiosis is identical to Osam1-1.

Figure 3 Meiosis of male meiocytes in wild type. (A) Early leptotene; (B) late leptotene; (C) zygotene; (D) pachytene; (E) diakinesis; (F) metaphase I; (G) anaphase I; (H) dyad; and (I) Tetrad. Scale bars, 5 μm. .

Expression

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Evolution

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Labs working on this gene

• State Key Laboratory of Plant Genomics and Center for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
• Key Laboratory of Plant Functional Genomics of Ministry of Education, Yangzhou University, Yangzhou 225009, China