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陕西快乐十分看号技巧:Constitutive signaling activity of a receptor-associated protein links fertilization with embryonic patterning in Arabidopsis thaliana
广东快乐十分投注下载 www.hmclip.net Edited by Dolf Weijers, Wageningen University, Wageningen, The Netherlands, and accepted by Editorial Board Member Caroline Dean January 28, 2019 (received for review September 13, 2018)
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In flowering plants, membrane-associated kinases of the BRASSINOSTEROID SIGNALING KINASE (BSK) family are ubiquitous, receptor-associated signaling partners in various receptor kinase pathways, where they function in signaling relay. The Brassicaceae-specific BSK family member SHORT SUSPENSOR (SSP), however, acts as a patterning cue in the zygote, initiating the apical-basal patterning process in a signal-like manner. The SSP protein has lost a regulatory, intramolecular interaction and activates the MAPKKK YODA signaling pathway constitutively, in principle, enabling the protein to initiate embryonic patterning without receptor activation. We further show that the BSK family members BSK1 and BSK2, both conserved in flowering plants, activate the same signaling pathway in parallel to SSP and might constitute remnants of an older, canonical signaling pathway still active in Arabidopsis.
In flowering plants, the asymmetrical division of the zygote is the first hallmark of apical-basal polarity of the embryo and is controlled by a MAP kinase pathway that includes the MAPKKK YODA (YDA). In Arabidopsis, YDA is activated by the membrane-associated pseudokinase SHORT SUSPENSOR (SSP) through an unusual parent-of-origin effect: SSP transcripts accumulate specifically in sperm cells but are translationally silent. Only after fertilization is SSP protein transiently produced in the zygote, presumably from paternally inherited transcripts. SSP is a recently diverged, Brassicaceae-specific member of the BRASSINOSTEROID SIGNALING KINASE (BSK) family. BSK proteins typically play broadly overlapping roles as receptor-associated signaling partners in various receptor kinase pathways involved in growth and innate immunity. This raises two questions: How did a protein with generic function involved in signal relay acquire the property of a signal-like patterning cue, and how is the early patterning process activated in plants outside the Brassicaceae family, where SSP orthologs are absent? Here, we show that Arabidopsis BSK1 and BSK2, two close paralogs of SSP that are conserved in flowering plants, are involved in several YDA-dependent signaling events, including embryogenesis. However, the contribution of SSP to YDA activation in the early embryo does not overlap with the contributions of BSK1 and BSK2. The loss of an intramolecular regulatory interaction enables SSP to constitutively activate the YDA signaling pathway, and thus initiates apical-basal patterning as soon as SSP protein is translated after fertilization and without the necessity of invoking canonical receptor activation.
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Author contributions: W.L., C.G., and M.B. designed research; A.N., E.E., L.Y.A., D.S., A.H., K.W., P.B., M.H., T.J.M., M.K., W.L., C.G., and M.B. performed research; A.N., E.E., L.Y.A., D.S., K.W., T.J.M., M.K., W.L., C.G., and M.B. analyzed data; and W.L., C.G., and M.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. D.W. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1815866116/-/DCSupplemental.
Published under the PNAS license.