HEXOKINASE 1 Control of Post-Germinative Seedling Growth

O_LIIn darkness, PHYTOCHROME INTERACTING FACTOR (PIF)-induced skotomorphogenic seedling growth, is exemplified by increased hypocotyl elongation. HEXOKINASE1 (HXK1), which is also implicated in seedling establishment, can operate as a glycolytic enzyme or as a glucose-activated sensor signalling molecule. Under light and nutrient limiting conditions, the HXK1 sensor-signalling has been shown to control hypocotyl elongation. Little is known of whether HXK1 glycolytic function, or HXK1 and PIF cross-talk, is required to control hypocotyl growth. C_LIO_LIWe demonstrate HXK1 glycolytic activity is critical for cell expansion, and hypocotyl growth, post-germination. Notably, application of glucose-6-phosphate, the HXK1 enzymatic product, can restore short gin2-1/hxk1-1 mutant hypocotyls to wild-type length. Further, HXK1 sensor-signalling complex components, VHA-B1 and RPT5B, do not contribute to this response, for unlike gin2-1/hxk1-1, the vha-B1 and rpt5b alleles only disrupt hypocotyl growth following exogenous glucose application. C_LIO_LImRNA-seq analysis illustrates that HXK1 and PIF signalling converge at genes with known roles in light signalling. HXK1 imposes strong regulation on chloroplast and mitochondrial encoded genes, also branched chain amino acid catabolism pathway genes, which can provide a source of respiratory substrates in starvation conditions. C_LIO_LIOur study establishes the importance of HXK1 enzymatic function in supporting cell expansion and hypocotyl growth. We demonstrate a degree of cross-talk between HXK1 and PIFs through common target gene set. C_LI