Ganpudi, A. | Search bioRxiv

bioRxiv2019

HEXOKINASE 1 Glycolytic Action Fuels 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

plant biology↗

bioRxiv2018

Dawn and photoperiod sensing by phytochrome A

In plants, light receptors play a pivotal role in photoperiod sensing, enabling them to track seasonal progression. Photoperiod sensing arises from an interaction between the plants endogenous circadian oscillator and external light cues. Here, we characterise the role of phytochrome A (phyA) in photoperiod sensing. Our meta-analysis of functional genomic datasets identified phyA as a principal transcriptional regulator of morning-activated genes, specifically in short photoperiods. We demonstrate that PHYA expression is under the direct control of the PHYTOCHROME INTERACTING FACTOR transcription factors, PIF4 and PIF5. As a result, phyA protein accumulates during the night, especially in short photoperiods. At dawn phyA activation by light results in a burst of gene expression, with consequences for anthocyanin accumulation. The combination of complex regulation of PHYA transcript and the unique molecular properties of phyA protein make this pathway a sensitive detector of both dawn and photoperiod.\n\nSignificance statementThe changing seasons subject plants to a variety of challenging environments. In order to deal with this, many plants have mechanisms for inferring the season by measuring the duration of daylight in a day. A number of well-known seasonal responses such as flowering are responsive to daylength or photoperiod. Here, we describe how the photoreceptor protein phytochrome A senses short photoperiods. This arises from its accumulation during long nights, as happens during winter, and subsequent activation by light at dawn. As a result of this response, the abundance of red anthocyanin pigments is increased in short photoperiods. Thus, we describe a mechanism underlying a novel seasonal phenotype in an important model plant species.

plant biology↗