10-day time-lapse imaging showed that young precursor cells undergo 6(!) rounds of asymmetric division oriented in a Fibonacci spiral. The first three divisions make non-stomatal cells before divisions 4 to 6 make the 3 subsidiary cells. Finally, a symmetric division makes the guard cell pair. 3/n - ThreadSky

heikelindner.bsky.social • 80 days ago

10-day time-lapse imaging showed that young precursor cells undergo 6(!) rounds of asymmetric division oriented in a Fibonacci spiral. The first three divisions make non-stomatal cells before divisions 4 to 6 make the 3 subsidiary cells. Finally, a symmetric division makes the guard cell pair. 3/n

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heikelindner.bsky.social•80 days ago

Gene-editing the two homologs of the core stomatal transcription factor MUTE disrupted stomatal formation and messed up asymmetric divisions - a first hint that Kalanchoë MUTE has a different role in leaf succulents than Arabidopsis. 4/n

heikelindner.bsky.social•80 days ago

Indeed, fluorescent reporter genes showed that both MUTE homologs are expressed specifically during the asymmetric divisions forming SCs. This suggested that MUTE might be involved in controlling SC divisions. 5/n

heikelindner.bsky.social•80 days ago

When overexpressing Kalanchoë MUTE, many additional subsidiary-cell-like cells were formed in Kalanchoë. This is strikingly different from the MUTE overexpression phenotype in Arabidopsis, where many additional guard cells pairs rather than subsidiary cells are formed. 6/n

heikelindner.bsky.social•80 days ago

This suggested that MUTE in the leaf succulent Kalanchoë makes subsidiary cells. Strikingly, this is more similar to MUTE’s role in the distantly related grasses than in the more closely related Arabidopsis. 7/n

heikelindner.bsky.social•80 days ago

Finally, we used transcriptomics to detect the deregulated downstream genes when Kalanchoë MUTE is overexpressed. Unlike in Arabidopsis, genes linked to asymmetric divisions are upregulated and genes linked to guard cell differentiation are downregulated. 8/n

heikelindner.bsky.social•80 days ago

Together, we propose that much like in grasses, Kalanchoë MUTE makes stomatal subsidiary cells by delaying the guard cell program and inducing an asymmetric division program. 9/n

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