Screening of low-light-tolerant potato varieties and cloning and functional analysis of the transcription factor gene StPIF3

Based on measurements and comparisons of growth traits, chlorophyll fluorescence parameters, and other related indices in nine potato varieties under low-light treatment, the cultivar “Atlantic” was identified as low-light tolerant by principal component analysis. To investigate genes involved in the low-light response of “Atlantic”, we performed transcriptome analysis after treatment with a light intensity of 10 μmol m⁻² s⁻¹ for 48 h. Using GO enrichment, KEGG pathway analysis, and transcription factor prediction, we identified the light-responsive transcription factor gene StPIF3 and cloned its full-length cDNA. StPIF3 was introduced into tobacco via agrobacterium-mediated transformation, and T₁ transgenic lines were obtained by selfing. Bioinformatics analysis, RT-qPCR, and chlorophyll fluorescence measurements were used to characterize and validate its function. StPIF3 encodes a 716-amino-acid protein with a predicted molecular weight of 76.77 kD and an isoelectric point of 7.26, and it is predicted to be hydrophilic and unstable. The StPIF3 protein contains a typical HLH domain and belongs to the bHLH family; phylogenetic analysis indicated that StPIF3 is most closely related to the tobacco homolog. Under 50 μmol m⁻² s⁻¹ light intensity, transgenic tobacco plants showed significantly higher Fv/Fm, qP, ETR, ETRmax, and SPAD values than wild-type plants, whereas F₀ was lower. Overall, overexpression of StPIF3 markedly improves electron transport and light energy use efficiency, thereby enhancing photosynthetic performance and low-light tolerance.