First a digitized scent. Then, a paper in Nature shows how odorant receptors can be engineered to figure out how slightly different structures can recognize very distinct molecules. This is the start of something big. I can...smell it.

A couple years ago, I wrote that plant synthetic biology is ~15 years behind microbial efforts. But now, the gap seems to be closing. For a new paper, researchers used integrases to record gene expression events in Arabidopsis, with single-cell resolution, to study how these plants develop from seed to maturity. This isn't the first paper to report a "memory switch" for plants (that happened back in 2020), but this paper does take it quite a bit further. The authors use two different integrases to track two different genes involved in lateral root development, called AHP6 and GATA23. The integrases enable them to figure out which gene turns on FIRST, and in which cells. They also did a similar experiment to study stomatal development. The integrases can trigger four different states: In state 0, cells express a blue fluorescent protein; this indicates that neither of the genes have yet been expressed. Now, if gene #1 is activated, one of the integrases switches on and makes the cells glow red. If the second gene is activated AFTER this event, then the second integrase also switches on and the cells glow green. If gene #2 is expressed before gene #1, however, the integrase instead makes an excision in the genome and the cells don't glow at all. By looking at how various cells in the plant glow, in different colors, scientists are able to figure out which genes are turned on which order. Cool stuff. I'm sure this can be scaled up, and more integrases can be added, to study even more genes in parallel.