Hexokinases (HXKs) and fructokinases (FRKs) are the only two families of enzymes in plants that have been identified as able to phosphorylate Glucose (Glc) and Fructose (Fru). Glc can only be phosphorylated in plants by HXKs, while Fru can be phosphorylated by either HXKs or FRKs. The various subcellular localizations of HXKs in plants indicate that they are involved in diverse functions, including anther dehiscence and pollen germination, stomatal closure in response to sugar levels, stomatal aperture and reducing transpiration. Its association with modulating programmed cell death, and responses to oxidative stress and pathogen infection (abiotic and biotic stresses) also have been reported. To extend our understanding about the function of HXK-like genes in the response of Prunus rootstocks to abiotic stress, we performed a detailed bioinformatic and functional analysis of hexokinase 3-like genes (HXK3s) from two Prunus rootstock genotypes, ‘M.2624’ (Prunus cerasifera Ehrh × P. munsoniana W.Wight & Hedrick) and ‘M.F12/1’ (P. avium L.), which are tolerant and sensitive to hypoxia stress, respectively. A previous large-scale transcriptome sequencing of roots of these rootstocks, showed that this HXK3-like gene that was highly induced in the tolerant genotype under hypoxia conditions. In silico analysis of gene promoters from M.2624 and M.F12/1 genotypes revealed regulatory elements that could explain differential transcriptional profiles of HXK3 genes. Subcellular localization was determinates by both bioinformatic prediction and expression of their protein fused to the green fluorescent protein (GFP) in protoplasts and transgenic plants of Arabidopsis. Both approaches showed that they are expressed in plastids. Metabolomics analysis of Arabidopsis plants ectopically expressing Prunus HXK3 genes revealed that content of several metabolites including phosphorylated sugars (G6P), starch and some metabolites associated with the TCA cycle were affected. These transgenic Arabidopsis plants showed improved tolerance to salt and drought stress under growth chamber conditions. Our results suggest that Prunus HXK3 is a potential candidate for enhancing tolerance to salt and drought stresses in stone fruit trees and other plants.

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The Chilean sweet cherry (Prunus avium (L.) L.) industry became the leading exporter worldwide. The bacterial canker is the most significant disease causing major economic losses. Pseudomonas syringae pv. syringae (Pss) is the only related pathovar recognized in Chile and it is mainly controlled with Cu-based antimicrobial compounds (CBAC). Soil contamination and the decreasing efficacy of CBACs by the emergence of Cu-resistant bacterial strains threaten the longterm sustainability of sweet cherry production. This study aimed at characterizing the bacterial community associated with canker infection injuries by assessing Cu resistance in sweet cherry orchards in the O'Higgins Region of Chile. Eighty bacteria isolates were obtained from tissue that presented bacterial canker symptoms from cherry trees. We assessed the production of fluorescent pigments in Fe-deficient media, presence of the housekeeping genes rpoD and cts, and presence of syringomycin-producing genes syrb and syrD. Their pathogenic ability was evaluated on immature sweet cherry fruits and Cu resistance was determined as the minimum inhibitory concentration (MIC) using CuSO4. Only five isolates were Cu-susceptible (MIC < 0.8 mM), while 75 isolates exhibited different levels of Cu resistance (MIC > 0.8 mM). At least one gene of the copABCD operon/or and its regulatory genes were detected in 17 isolates, suggesting that most isolates likely have different mechanisms of Cu tolerance. Six isolates were identified as Pss, presenting different degrees of Cu resistance, but all presented at least one feature of the copABCD operon. A bacterial community that presents high Cu-resistance, probably under control of diverse genetic mechanisms, decreases the efficacy of CBAC.