State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, 310058, China.
Division of Biochemistry, Interdisciplinary Plant Group, Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA.
Plant J. 2017 Dec;92(6):1005-1019. doi: 10.1111/tpj.13737. Epub 2017 Nov 11.
In flowering plants, developing embryos reside in maternal sporophytes. It is known that maternal generation influences the development of next-generation embryos; however, little is known about the signaling components in the process. Previously, we demonstrated that Arabidopsis mitogen-activated protein kinase 6 (MPK6) and MPK3 play critical roles in plant reproduction. In addition, we noticed that a large fraction of seeds from mpk6 single-mutant plants showed a wrinkled seed coat or a burst-out embryo phenotype. Here, we report that these seed phenotypes can be traced back to defective embryogenesis. The defective embryos have shorter suspensors and reduced growth along the longitudinal axis. Furthermore, the cotyledons fail to bend over to progress to the bent-cotyledon stage. As a result of the uneven circumference along the axis, the seed coat wrinkles to develop raisin-like morphology after dehydration. In more severe cases, the embryo can be pushed out from the micropylar end, resulting in the burst-out embryo seed phenotype. Genetic analyses demonstrated that the defective embryogenesis of the mpk6 mutant is a maternal effect. Heterozygous or homozygous mpk6 embryos have defects only in mpk6 homozygous maternal plants, but not in wild-type or heterozygous maternal plants. The loss of function of MKK4/MKK5 also results in the same phenotypes, suggesting that MKK4/MKK5 might act upstream of MPK6 in this pathway. The maternal-mediated embryo defects are associated with changes in auxin activity maxima and PIN localization. In summary, this research demonstrates that the Arabidopsis MKK4/MKK5-MPK6 cascade is an important player in the maternal control of embryogenesis.
在开花植物中，发育中的胚胎位于母体孢子体中。已知母体世代会影响下一代胚胎的发育；然而，关于这个过程中的信号成分知之甚少。以前，我们证明了拟南芥丝裂原活化蛋白激酶 6（MPK6）和 MPK3 在植物繁殖中起着关键作用。此外，我们注意到，mpk6 单突变体植物的大量种子表现出皱缩的种皮或爆裂的胚胎表型。在这里，我们报告说这些种子表型可以追溯到胚胎发生缺陷。缺陷胚胎的悬浮体较短，沿纵轴的生长减少。此外，子叶不能弯曲到弯曲子叶阶段。由于轴周围的周长不均匀，种皮起皱，在脱水后发育成葡萄干状形态。在更严重的情况下，胚胎可以从珠孔端被推出，导致爆裂的胚胎种子表型。遗传分析表明，mpk6 突变体的胚胎发生缺陷是母体效应。杂合或纯合 mpk6 胚胎仅在纯合 mpk6 母本植物中存在缺陷，而在野生型或杂合母本植物中不存在缺陷。MKK4/MKK5 的功能丧失也会导致相同的表型，这表明 MKK4/MKK5 可能在该途径中上游作用于 MPK6。母体介导的胚胎缺陷与生长素活性最大值和 PIN 定位的变化有关。总之，这项研究表明，拟南芥 MKK4/MKK5-MPK6 级联是母体控制胚胎发生的重要参与者。
