Kosugi Shunichi, Ohashi Yuko
Plant Physiology Department, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan.
Plant Physiol. 2003 Aug;132(4):2012-22. doi: 10.1104/pp.103.025080.
The E2F family plays a pivotal role in cell cycle control and is conserved among plants and animals, but not in fungi. This provides for the possibility that the E2F family was integrated during the development of higher organisms, but little is known about this. We examined the effect of E2F ectopically expressed in transgenic tobacco (Nicotiana tabacum) plants on growth and development using E2Fa (AtE2F3) and DPa from Arabidopsis. E2Fa-DPa double transgenic lines exhibited altered phenotypes with curled leaves, round shaped petals, and shortened pistils. In mature but not immature leaves of the double transgenic lines, there were enlarged nuclei with increasing ploidy levels accompanied by the ectopic expression of S phase- but not M phase-specific genes. This indicates that a high expression of E2F promotes endoreduplication by accelerating S phase entry in terminally differentiated cells with limited mitotic activity. Furthermore, mature leaves of the transgenic plants contained increased numbers of small cells, especially on the palisade (adaxial) side of the outer region toward the edge, and the leaf strips exhibited hormone-independent callus formation when cultured in vitro. These observations suggest that an enhanced E2F activity modulates cell cycle in a cell type-specific manner and affects plant morphology depending on a balance between activities for committing to S phase and M phase, which likely differ between organs or tissues.
E2F家族在细胞周期调控中起关键作用，在植物和动物中保守，但在真菌中不存在。这为E2F家族在高等生物发育过程中整合的可能性提供了依据，但对此知之甚少。我们利用拟南芥的E2Fa（AtE2F3）和DPa，研究了在转基因烟草（Nicotiana tabacum）植株中异位表达的E2F对生长发育的影响。E2Fa-DPa双转基因系表现出叶片卷曲、花瓣圆形和雌蕊缩短等表型改变。在双转基因系的成熟叶片而非未成熟叶片中，存在核增大且倍性水平增加的情况，同时伴有S期而非M期特异性基因的异位表达。这表明E2F的高表达通过加速有丝分裂活性有限的终末分化细胞进入S期来促进核内复制。此外，转基因植株的成熟叶片含有更多数量的小细胞，尤其是在靠近边缘的外层区域的栅栏（近轴）侧，并且叶片条在体外培养时表现出激素非依赖性愈伤组织形成。这些观察结果表明，增强的E2F活性以细胞类型特异性方式调节细胞周期，并根据进入S期和M期的活性之间的平衡影响植物形态，而这种平衡在不同器官或组织中可能有所不同。
