Constitutive signaling activity of a receptor-associated protein links fertilization with embryonic patterning in Arabidopsis thaliana ($) (PNAS)

The apical and basal identity of a growing embryo is determined by an asymmetrical division of the zygote in flowering plants. The MAPKK kinase YODA (YDA) is important for zygotic elongation and embryonic polarity. During embryo development, YDA is activated by the membrane associated pseudo-kinase SHORT SUSPENSOR (SSP), which belongs to BRASSINOSTEROID SIGNALING KINASE (BSK) family and expresses specifically in sperm cells of pollen. SSP is unusual in that it constitutively activates YDA. The authors’ studies suggest that the delivery of SSP during fertilization is sufficient to activate YDA and establish apical-basal polarity in the embryo. By losing a regulatory interaction SSP can constitutively activates YDA. Additionally, BSK1 and BSK2 work independently to SSP to genetically control the YDA role in early embryonic development. (Summary by Kaushal Kumar Bhati) PNAS