Wang Huachun, Liu Yidong, Bruffett Kristin, Lee Justin, Hause Gerd, Walker John C, Zhang Shuqun
Department of Biochemistry and Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211, USA.
Plant Cell. 2008 Mar;20(3):602-13. doi: 10.1105/tpc.108.058032. Epub 2008 Mar 25.
The plant life cycle includes diploid sporophytic and haploid gametophytic generations. Female gametophytes (embryo sacs) in higher plants are embedded in specialized sporophytic structures (ovules). Here, we report that two closely related mitogen-activated protein kinases in Arabidopsis thaliana, MPK3 and MPK6, share a novel function in ovule development: in the MPK6 mutant background, MPK3 is haplo-insufficient, giving female sterility when heterozygous. By contrast, in the MPK3 mutant background, MPK6 does not show haplo-insufficiency. Using wounding treatment, we discovered gene dosage-dependent activation of MPK3 and MPK6. In addition, MPK6 activation is enhanced when MPK3 is null, which may help explain why mpk3(-/-) mpk6(+/-) plants are fertile. Genetic analysis revealed that the female sterility of mpk3(+/-) mpk6(-/-) plants is a sporophytic effect. In mpk3(+/-) mpk6(-/-) mutant plants, megasporogenesis and megagametogenesis are normal and the female gametophyte identity is correctly established. Further analysis demonstrates that the mpk3(+/-) mpk6(-/-) ovules have abnormal integument development with arrested cell divisions at later stages. The mutant integuments fail to accommodate the developing embryo sac, resulting in the embryo sacs being physically restricted and female reproductive failure. Our results highlight an essential function of MPK3 and MPK6 in promoting cell division in the integument specifically during ovule development.
植物生命周期包括二倍体孢子体世代和单倍体配子体世代。高等植物中的雌配子体（胚囊）嵌入在特殊的孢子体结构（胚珠）中。在此，我们报道拟南芥中两个密切相关的丝裂原活化蛋白激酶MPK3和MPK6在胚珠发育中具有一项新功能：在MPK6突变背景下，MPK3单倍体不足，杂合时导致雌性不育。相比之下，在MPK3突变背景下，MPK6未表现出单倍体不足。通过创伤处理，我们发现了MPK3和MPK6的基因剂量依赖性激活。此外，当MPK3缺失时，MPK6的激活增强，这可能有助于解释为什么mpk3(-/-) mpk6(+/-)植株是可育的。遗传分析表明，mpk3(+/-) mpk6(-/-)植株的雌性不育是一种孢子体效应。在mpk3(+/-) mpk6(-/-)突变植株中，大孢子发生和雌配子体发生正常，雌配子体身份得以正确确立。进一步分析表明，mpk3(+/-) mpk6(-/-)胚珠的珠被发育异常，后期细胞分裂停滞。突变的珠被无法容纳发育中的胚囊，导致胚囊受到物理限制，雌性生殖失败。我们的结果突出了MPK3和MPK6在胚珠发育过程中特别是促进珠被细胞分裂方面的重要功能。
