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Haplo-Insufficiency of MPK3 in MPK6 Mutant Background Uncovers a Novel Function of These Two MAPKs in Arabidopsis Ovule Development

Huachun Wang, Yidong Liu, Kristin Bruffett, Justin Lee, Gerd Hause, John C. Walker and Shuqun Zhang
The Plant Cell
Vol. 20, No. 3 (Mar., 2008), pp. 602-613
Stable URL: http://www.jstor.org/stable/20077310
Page Count: 12
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Haplo-Insufficiency of MPK3 in MPK6 Mutant Background Uncovers a Novel Function of These Two MAPKs in Arabidopsis Ovule Development
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Abstract

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.

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