I have been a bit remiss in updating the website but thought I would mention this one while I’m on here: the latest publication from the lab is recently published in New Phytologist, Hugh Yao as first author with valuable contributions from Frank and Kim as well. We think KAI2 proteins prefer to work with butenolide compounds that lack a methyl group, versus D14 proteins that require a methyl group. We used a couple of different compounds – GR24 and nitrile debranones – and showed that if you remove their respective methyl groups, they become much more active through KAI2. And most importantly, they become *specific* for KAI2 – they do not activate D14. So now we have a specific molecular feature that can be used to manipulate KAI2-dependent signalling. Most excellent.

Andy has officially started his PhD, yay! Good luck Andy, and work like stink.

Hugh, will you ever come back from exile in China so we can have four PhD students in the lab at once??

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!

We are very proud to announce the publication of our latest work, “Divergent receptor proteins confer responses to different karrikins in two ephemeral weeds“, by Kelly Sun, Jiaren Yao et al. in Nature Communications. The work behind this paper started when Kelly was an Honours student, and Mark a post-doc in Steve Smith’s lab, in 2014. From very humble beginnings the project grew, stalled, went into reverse, and then when a clear story began to emerge, we started to work on it in earnest. This project had its fair share of frustrations, but we’re pretty happy with how it turned out in the end.

In summary, we found that Saharan mustard (Brassica tournefortii) – an invasive weed found throughout the southern half of Australia – has a specialised version of KAI2 that allows the plant to perceive KAR1 more sensitively than other plants such as Arabidopsis. We identified the amino acid changes that are responsible for this change in ligand specificity, and also found similar changes in other species as well, suggesting that changes in KAI2 function may have occurred multiple times during the evolution of flowering plants.

You can read the UWA press release describing our findings here.

The map shows the distribution of sightings of this pernicious weed in Australia. You will often find it in disturbed habitats. Here in Perth, it’s frequently seen on land cleared for building, down sandy laneways and along fence lines. There’s also populations in Kings Park and Bold Park. In short, it’s everywhere, it’s very hardy, and it germinates very robustly after a fire because of its Karrikin response. See the full entry for B. tournefortii at the Atlas of Living Australia.