Kojima Koji, Tamura Junya, Chiba Hiroto, Fukada Kanae, Tsukaya Hirokazu, Horiguchi Gorou
Department of Life Science, College of Science, Rikkyo University, Tokyo, Japan.
Graduate School of Science, The University of Tokyo, Tokyo, Japan.
Front Plant Sci. 2018 Jan 9;8:2240. doi: 10.3389/fpls.2017.02240. eCollection 2017.
Leaf abaxial-adaxial patterning is dependent on the mutual repression of leaf polarity genes expressed either adaxially or abaxially. In , this process is strongly affected by mutations in ribosomal protein genes and in ribosome biogenesis genes in a sensitized genetic background, such as (). Most ribosome-related mutants by themselves do not show leaf abaxialization, and one of their typical phenotypes is the formation of pointed rather than rounded leaves. In this study, we characterized two ribosome-related mutants to understand how ribosome biogenesis is linked to several aspects of leaf development. Previously, we isolated () which exhibits the pointed-leaf phenotype and has a cell proliferation defect. encodes a homolog of Nop2 in , a ribosome biogenesis factor involved in pre-60S subunit maturation. In this study, we found another pointed-leaf mutant that carries a mutation in a gene encoding an uncharacterized protein with a G-patch domain. Similar to , this mutant, named (), has a reduced number of leaf cells. In addition, double mutants showed a strong genetic interaction such that they synergistically impaired cell proliferation in leaves and produced markedly larger cells. On the other hand, they showed additive phenotypes when combined with several known ribosomal protein mutants. Furthermore, these mutants have a defect in pre-rRNA processing. and are strongly expressed in tissues with high cell proliferation activity, and GDP1-GFP and GFP-OLI2 are localized in the nucleolus. These results suggest that OLI2 and GDP1 are involved in ribosome biogenesis. We then examined the effects of and on adaxial-abaxial patterning by crossing them with . Interestingly, neither nor strongly enhanced the leaf polarity defect of . Similar results were obtained with triple mutants although they showed severe growth defects. These results suggest that the leaf abaxialization phenotype induced by ribosome-related mutations is not merely the result of a general growth defect and that there may be a sensitive process in the ribosome biogenesis pathway that affects adaxial-abaxial patterning when compromised by a mutation.
叶片近轴-远轴模式形成依赖于在近轴面或远轴面表达的叶片极性基因之间的相互抑制。在[具体植物名称]中，在如[具体植物名称]的敏感遗传背景下，核糖体蛋白基因和核糖体生物发生基因的突变会强烈影响这一过程。大多数与核糖体相关的突变体自身并不表现出叶片远轴化，其典型表型之一是形成尖形而非圆形叶片。在本研究中，我们对两个与核糖体相关的突变体进行了表征，以了解核糖体生物发生如何与叶片发育的多个方面相关联。此前，我们分离出了[突变体名称]（[具体植物名称]），其表现出尖叶表型且具有细胞增殖缺陷。[基因名称]编码[具体植物名称]中Nop2的同源物，Nop2是一种参与前60S亚基成熟的核糖体生物发生因子。在本研究中，我们发现了另一个尖叶突变体，其在编码具有G-结构域的未表征蛋白的基因中发生了突变。与[突变体名称]类似，这个名为[突变体名称]（[具体植物名称]）的突变体叶片细胞数量减少。此外，[两个突变体名称]双突变体表现出强烈的遗传相互作用，使得它们协同损害叶片中的细胞增殖并产生明显更大的细胞。另一方面，当它们与几个已知的核糖体蛋白突变体组合时，表现出累加表型。此外，这些突变体在前体rRNA加工方面存在缺陷。[基因名称]和[基因名称]在具有高细胞增殖活性的组织中强烈表达，并且GDP1-GFP和GFP-OLI2定位于核仁。这些结果表明OLI2和GDP1参与核糖体生物发生。然后，我们通过将它们与[具体植物名称]杂交来研究[基因名称]和[基因名称]对近轴-远轴模式形成的影响。有趣的是，[突变体名称]和[突变体名称]都没有强烈增强[具体植物名称]的叶片极性缺陷。[三个突变体名称]三突变体尽管表现出严重的生长缺陷，但也得到了类似的结果。这些结果表明，核糖体相关突变诱导的叶片远轴化表型不仅仅是一般生长缺陷的结果，并且在核糖体生物发生途径中可能存在一个敏感过程，当因突变而受损时会影响近轴-远轴模式形成。
