It was a behemoth, but Aashima Khosla, Dave Nelson and team at UC Riverside have published a tour de force analysing the functional domains of SMAX1, and showing how it is degraded in response to Karrikins and GR24. Jiaren (Hugh) and I contributed by showing that KAI2 degradation was dependent on SMAX1 and SMXL2, suggesting that the receptor and downstream repressor proteins form a complex and are possibly degraded together.
It was a pleasure to be part of this work – and congratulations to Aashima, Dave and others for an enormous effort that finally paid off. It’s rare to see such an admission in a manuscript, but I quote verbatim from the final paragraph of the introduction: “This proved to be an unexpectedly difficult undertaking”. Indeed it was.
Read the paper in The Plant Cell here. Here’s the full citation:
Khosla, A., Morffy, N., Li, Q., Faure, L., Chang, S., Yao, J., Zheng, J., Cai, M., Stanga, JP., Flematti, GR., Waters, MT., Nelson, DC. (2020). Structure-Function Analysis of SMAX1 Reveals Domains that Mediate its Karrikin-Induced Proteolysis and Interaction with the Receptor KAI2. The Plant cell https://dx.doi.org/10.1105/tpc.19.00752
Our manuscript comes at a time of a veritable flurry of SMAX1 and SMXL-related publications from other groups, namely:
Wang, L., Xu, Q., Yu, H., Ma, H., Li, X., Yang, J., Chu, J., Xie, Q., Wang, Y., Smith, S., Li, J., Xiong, G., Wang, B. (2020). Strigolactone and Karrikin Signaling Pathways Elicit Ubiquitination and Proteolysis of SMXL2 to Regulate Hypocotyl Elongation in Arabidopsis thaliana. The Plant Cell https://dx.doi.org/10.1105/tpc.20.00140
Bunsick, M., Toh, S., Wong, C., Xu, Z., Ly, G., McErlean, C., Pescetto, G., Nemrish, K., Sung, P., Li, J., Scholes, J., Lumba, S. (2020). SMAX1-dependent seed germination bypasses GA signalling in Arabidopsis and Striga Nature Plants https://dx.doi.org/10.1038/s41477-020-0653-z
Wang, L., Wang, B., Yu, H., Guo, H., Lin, T., Kou, L., Wang, A., Shao, N., Ma, H., Xiong, G., Li, X., Yang, J., Chu, J., Li, J.(2020). Transcriptional regulation of strigolactone signalling in Arabidopsis Nature https://dx.doi.org/10.1038/s41586-020-2382-x
Choi, J., Lee, T., Cho, J., Servante, E., Pucker, B., Summers, W., Bowden, S., Rahimi, M., An, K., An, G., Bouwmeester, H., Wallington, E., Oldroyd, G., Paszkowski, U. (2020). The negative regulator SMAX1 controls mycorrhizal symbiosis and strigolactone biosynthesis in rice. Nature Communications 11(1), 2114. https://dx.doi.org/10.1038/s41467-020-16021-1
This corpus of work represents one of the biggest leaps forward in this field for some time, and constitutes a considerable collective achievement. Congratulations to everyone!