Guard cells control hypocotyl elongation through HXK1, HY5, and PIF4

Gilor Kelly, Danja Brandsma, Aiman Egbaria, Ofer Stein, Adi Doron-Faigenboim, Nitsan Lugassi, Eduard Belausov, Hanita Zemach, Felix Shaya, Nir Carmi, Nir Sade, David Granot*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


The hypocotyls of germinating seedlings elongate in a search for light to enable autotrophic sugar production. Upon exposure to light, photoreceptors that are activated by blue and red light halt elongation by preventing the degradation of the hypocotyl-elongation inhibitor HY5 and by inhibiting the activity of the elongation-promoting transcription factors PIFs. The question of how sugar affects hypocotyl elongation and which cell types stimulate and stop that elongation remains unresolved. We found that overexpression of a sugar sensor, Arabidopsis hexokinase 1 (HXK1), in guard cells promotes hypocotyl elongation under white and blue light through PIF4. Furthermore, expression of PIF4 in guard cells is sufficient to promote hypocotyl elongation in the light, while expression of HY5 in guard cells is sufficient to inhibit the elongation of the hy5 mutant and the elongation stimulated by HXK1. HY5 exits the guard cells and inhibits hypocotyl elongation, but is degraded in the dark. We also show that the inhibition of hypocotyl elongation by guard cells’ HY5 involves auto-activation of HY5 expression in other tissues. It appears that guard cells are capable of coordinating hypocotyl elongation and that sugar and HXK1 have the opposite effect of light on hypocotyl elongation, converging at PIF4.

Original languageEnglish
Article number765
JournalCommunications Biology
Issue number1
StatePublished - Dec 2021


Dive into the research topics of 'Guard cells control hypocotyl elongation through HXK1, HY5, and PIF4'. Together they form a unique fingerprint.

Cite this