What is it about?

A plant’s basic body plan begins with its first embryonic cell. This study shows that three proteins—BSL1, BSL2, and BSL3—help this cell grow in the right direction and divide into two cells with different developmental roles. Without these proteins, embryos lose their normal organization. The proteins support a key cellular communication system called MAP kinase signaling, independently of the plant hormone brassinosteroid. Surprisingly, the related protein BSU1 is not required. The findings reveal a new mechanism for organizing early plant development and challenge previous ideas about the BSL protein family.

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Why is it important?

### Why is it important? The first division of a plant embryo helps determine which end will form the shoot and which will form the root. This study identifies BSL proteins as essential players in that early decision and reveals a previously unknown way they control MAP kinase signaling. It also challenges the widely accepted idea that these proteins mainly function in brassinosteroid hormone signaling. By improving our understanding of how plants establish their body plan, the findings provide a stronger foundation for future research on plant growth, development, and reproduction.

Perspectives

Future research can determine exactly how BSL proteins regulate MAP kinase activity and whether they act directly on MPK3 and MPK6 or through other proteins. It will also be important to learn whether this mechanism operates in other plant tissues and crop species. More broadly, these findings invite researchers to reconsider the established roles of the BSU1/BSL protein family and explore how the same proteins can control different signaling pathways in different developmental contexts.

Professor Magdy Alabady
University of Georgia

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This page is a summary of: Arabidopsis BSL phosphatases regulate zygote polarity through a brassinosteroid-independent essential function in MAP kinase signaling, Proceedings of the National Academy of Sciences, July 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2532666123.
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