Synchronised flowers
Plants synchronise the opening of their flowers with the scent production of those flowers. But how this is regulated is still not completely clear. Now a group of Korean researchers found the circadian gene that coordinates this synchrony.
The flowers of the coyote tobacco (Nicotiana attenuata) have a clear distinct rhythm. When they are ready, they open only at night for two, maybe three nights in a row. They close again during the day. In addition, at night, when they are open, the flowers emit benzylacetone to attract pollinators like the hawkmoths.
In order to find out how the plant regulates this, the researchers created two mutant plants that missed a functional clock gene. The first, missing LHY, opened its flowers two hours ahead of schedule. The second, missing ZTL, kept to the schedule, but only partially opened its flowers and emitted hardly any scent.
Master regulator
Using these two mutants the researchers then set out to find the gene that regulates LHY, ZTL, flower opening and scent emission. They did this by looking at the genes that were active during the time of flower opening and scent emission under normal conditions, but not in the LHY and ZTL missing plants. This allowed them to narrow the possible genes down to two: COL5 and BBX24.
To find out which of the two was the likely master switch, the researchers looked at where in the plant they were active. Finding that BBX24 was active in the stem, leaves, pedicel, and style. COL5 in contrast was mainly active in the corella, also called petals. As it are the petals that move when flowers open, the researchers investigated COL5 further.
The researchers subsequently analysed plants without COL5. Finding that these just like plants missing ZTL, plants missing COL5 did not completely open their flowers. They also produced hardly any scent. The reason behind the only partial opening of the flowers turned out to be that the cells on the inside of the petal (when the flower was closed) of plants without COL5 did not stretch that much during the opening of the flower as they did in plants with COL5. This restricted the movement of the petals.
Also in Petunia
Lastly the researchers wanted to find out if COL5 has a similar function in related plants. Therefore, the researchers looked up this gene in petunia. Petunia flowers, like those of coyote tobacco, emit scent during the night. Although the flowers once opened don’t close during the day. When the researchers created COL5 missing petunia plants, they found that these plants also had a reduced scent production during the night.
Moreover, by studying the flowers of petunia more closely, the researchers found that petunias do move the petals of their flowers in a day and night rhythm. At night the petals are curved backwards, as if the plant likes to open its flower even more than it already is. Sowing that petunia, just as coyote tobacco, synchronises its flower opening with scent emission.
Literature
Yuri Choi, Moonyoung Kang, Hyeonjin Kim, Taein Kim, Eunae Park, Jumi Kim, Hyunwoo Kim, Hyejung Yun, Hangah Lim, Youngbin Oh, Giltsu Choi, Sang-Gyu Kim, CONSTANS-LIKE 5 facilitates flower opening and scent biosynthesis in Solanaceae, The Plant Cell, Volume 38, Issue 2, February 2026, koag016, https://doi.org/10.1093/plcell/koag016
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