HEXOKINASE 1 Control of Post-Germinative Seedling Growth

Abstract

1 5 HEXOKINASE 1 (HXK1) is an evolutionarily conserved glycolytic enzyme that has a 1 6 separate nuclear glucose-sensor signalling function. In Arabidopsis, HXK1 mutant seedlings 1 7 have a stunted growth defect, yet how this relates to HXK1 function remains inconclusive. 1 8We show that the HXK1-glycolytic pathway performs a fundamental role in catabolising seed 1 9 reserves to fuel post-germinative cell division and expansion. This function is particularly 2 0 important in dim light which delays the switch to photoautotrophic growth. RNAseq analysis 2 1 reveals that HXK1 imposes strong repressive control on plastome gene expression, and 2 2 regulates nuclear-encoded genes that drive energy-consuming processes. Earlier studies 2 3 have implicated HXK1 sensor-signalling in the repression of CAB2 and CAA gene 2 4 expression by exogenous glucose. We show that over a wide range of irradiances this 2 5 pathway is not operative in seedlings. Our study therefore defines a new operational model 2 6for HXK1 action in catabolising carbon resources and tuning gene expression to optimize 2 7 seedling growth. 2 8 2 9

A reactive oxygen species Ca2+ signalling pathway identified from a chemical screen for modifiers of sugar‐activated circadian gene expression

“…Nevertheless, more than two‐thirds of DEGs in chemical‐treated seedlings vs controls have been previously reported as sugar‐regulated genes (Fig. S9b ) (Xiong et al ., 2013 ; Ganpudi et al ., 2019 ; Peixoto et al ., 2021 ; Román et al ., 2021 ). This suggests that these four chemicals all have a major influence on sugar signalling or metabolism.…”

“…5c ). Branched‐chain amino acids valine, leucine and isoleucine have been associated with HXK1 (Ganpudi et al ., 2019 ) and TOR signalling (Cao et al ., 2019 ) but we did not detect notable changes for any chemical (Fig. 5d ).…”

A ROS-Ca2+ signalling pathway identified from a chemical screen for modifiers of sugar-activated circadian gene expression

“…Nevertheless, more than two thirds of DEGs in chemical-treated seedlings verusus controls have been previously reported as sugar-regulated genes (Fig. S7b) (Xiong et al ., 2013; Ganpudi et al ., 2019; Román et al ., 2021; Peixoto et al ., 2021). PATHOGEN AND CIRCADIAN CONTROLLED 1 (PCC1) , which is upregulated after dawn, was identified as a DEG for DPI, PI and AEG3482, but not Tyrphostin AG879, providing further support that Tyrphostin AG879 acts on a distinct signalling pathway.…”

“…We observed significant increases in tricarboxylic acid (TCA) cycle intermediates, particularly citrate and malate, with the magnitude of the effect increasing with time for all four chemicals (Fig 5c). Branched-chain amino acids valine, leucine and isoleucine have been associated with HXK1 (Ganpudi et al ., 2019) and TOR signalling (Cao et al ., 2019) but we did not detect notable changes for any chemical (Fig. 5d).…”

“…(b) List of differentially expressed genes between DMSO or chemical-treated seedlings. Genes previously identified as differentially expressed in dark-adapted seedlings treated with sucrose (Sugar; Román et al 2021) or in mutants of SnRK1 ( sesqui; Peixoto et al 2021), TOR ( tor ; Xiong et al 2013) or HXK1 ( gin2; Ganpudi et al 2019) are indicated by yellow (down-regulated) or blue (up-regulated). (c) Luciferase luminescence in DIN6p:LUC seedlings treated with DMSO or chemical before dusk (ZT11) (means ± SEM, n = 6).…”