FONDAP Center for Genome Regulation, Millennium Institute for Integrative Biology (iBio), Departamento de Genética Molecular y Microbiología, Pontificia Universidad Católica de Chile, Santiago 8331150, Chile.
Millennium Institute for Integrative Biology (iBio), Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia 5090000, Chile.
Curr Biol. 2020 Jun 8;30(11):1988-2000.e3. doi: 10.1016/j.cub.2020.03.036. Epub 2020 Apr 16.
Precise coordination of cell expansion and cell proliferation underlies growth in multicellular organisms. In addition to endogenous developmental programs, external environmental signals are integrated to modulate organ growth in plants. Nitrate is a nitrogen nutrient that can act as a potent signal to modulate shoot growth, yet the molecular mechanisms involved are largely unexplored in Arabidopsis thaliana or other plant species. Herein, we show that nitrate regulates vegetative growth by modulating cell size and endoreplication. We identified the LGO gene, a CDK inhibitor, as a key cell cycle regulatory factor influencing ploidy and cell-size depending on external nitrate. Nitrate induces LGO gene expression as early as 3 days after germination in epidermal and mesophyll cell layers, which undergo endoreplication to increment DNA content and cell size. Our results support a dual role for LGO on endoreplication and cell expansion. Surprisingly, although endoreplication and cell size are greatly reduced in lgo-2 mutant plants and increased in LGO-OX plants, cotyledon size remains unchanged relative to wild type and is set by the amount of nitrate. In lgo-2 mutant plants where cells are unable to endoreplicate fully, cotyledon organ size is achieved through cell division. We conclude nitrate generally controls cotyledon and leaf size by increasing ploidy levels and cell expansion but that cell division can substitute for endoreplication without affecting final organ size or growth in plants.
精确的细胞扩张和增殖协调是多细胞生物生长的基础。除了内源性发育程序外，外部环境信号也被整合来调节植物的器官生长。硝酸盐是一种氮营养物质，可以作为一种有效的信号来调节植物的生长，然而，在拟南芥或其他植物物种中，涉及的分子机制在很大程度上仍未被探索。在此，我们表明硝酸盐通过调节细胞大小和核内有丝分裂来调节营养生长。我们鉴定了 LGO 基因，一种 CDK 抑制剂，作为一个关键的细胞周期调节因子，根据外部硝酸盐的水平影响倍性和细胞大小。硝酸盐在萌发后 3 天内诱导 LGO 基因在表皮和叶肉细胞层中的表达，这些细胞经历核内有丝分裂以增加 DNA 含量和细胞大小。我们的结果支持 LGO 在核内有丝分裂和细胞扩张中的双重作用。令人惊讶的是，尽管 lgo-2 突变体植物中的核内有丝分裂和细胞大小大大减少，而 LGO-OX 植物中的核内有丝分裂和细胞大小增加，但与野生型相比，子叶大小保持不变，并且由硝酸盐的量决定。在 lgo-2 突变体植物中，细胞不能完全进行核内有丝分裂，子叶器官的大小是通过细胞分裂实现的。我们得出结论，硝酸盐通常通过增加倍性水平和细胞扩张来控制子叶和叶片的大小，但细胞分裂可以替代核内有丝分裂而不影响最终器官大小或植物的生长。
