Towards the functional characterization of apple (Malus domestica, cv. Granny smith) transcriptional responses to low oxygen: focus on a hypoxia inducible bHLH transcription factor

Apple, as one of the most commonly used fruits in the food industry, has been the subject of intensive research in the last century to prolong its shelf life and minimize postharvest losses. In current times, the industry standard for apple storage is the adoption of extremely low atmospheric oxygen concentration and low temperature, with its goal being to reduce the naturally occurring metabolic, ripening and aging processes. The effectiveness of storage in extreme hypoxia - due to modulation of intrinsic metabolic pathways in the fruit - is tied to a complex network of gene expression rearrangements, with many known and not yet characterized genes contributing to delayed fruit senescence. bHLH transcription factors (basic Helix-Loop-Helix proteins) are among the group of molecules which role in apple has not yet been thoroughly described. An apple’s bHLH transcription factor encoded by gene MdbHLH061 (MD08G1207700) has been chosen as the focus of this work, being involved in responses to low oxygen and for its similarity to the gene AtbHLH093 (AT5G65640) from Arabidopsis thaliana. Two transgenic lines of Arabidopsis thaliana (GG201 and GG203), transformed to overexpress MdbHLH061 in its wild type and mutated version, respectively, were genetically and phenotypically characterized. After confirming that the lines overexpressed the gene, a series of experiments were conducted to characterize the phenotype of genetically transformed plants and to lay the foundation towards understanding the function of the apple MdbHLH061 transcription factor in hypoxic responses.