PMC

Expression heatmap of StbHLH genes under salt, drought and heat stress. FPKM values of StbHLH genes were transformed by log2, and the heatmap was constructed with HemI. The clustering tree was constructed by hierarchical clustering using average linkage method.

Gene ontology (GO) annotation of StbHLH proteins. The annotation was performed on three categories, (A) molecular function, (B) biological process and (C) cellular component.

Phylogenetic tree of Arabidopsis and potato bHLH proteins. The phylogenetic tree was constructed using the Neighbor-joining method with 1000 bootstrap replications. The 15 subfamilies are marked with different colors. The circles represent potato bHLH proteins, and the rectangles represents Arabidopsis bHLH proteins.

Chromosomal distribution and gene duplications of StbHLHs. The tandem duplicated genes are represented by red rectangles, and the segmental duplicated genes are linked by orange lines. The scale bar on the left indicated the length (Mb) of potato chromosomes.

Expression heatmap of StbHLH genes in different tissues and organs. Fragments per kilobase of transcript per million mapped reads (FPKM) values of StbHLH genes were transformed by log2, and the heatmap was constructed with HemI. The clustering tree was constructed by hierarchical clustering using the average linkage method.

Expression profiles of StbHLH genes in various tissues. Quantitative RT-PCR was used to investigate the expression levels of StbHLH genes, and the results are represented by means ± standard deviations. The relative expression level was calculated by 2^−ΔCT method comparing with that of ef1α.

Expression levels of StbHLH genes under heat, salt and drought stress. Quantitative RT-PCR was used to investigate the expression levels of StbHLH genes, and the results are represented by means ± standard deviations. The relative expression levels of StbHLH genes under different abiotic stresses are compared with that of the control (CK).

Gene structures of Solanum tuberosum basic/helix–loop–helix (StbHLH) genes and phylogenetic relationships, conserved motifs of StbHLH proteins. (A) Phylogenetic tree of 124 StbHLH proteins. The unrooted Neighbor-joining phylogenetic tree was constructed with MEGA6 [] software using the full-length amino acid sequences of 124 StbHLH proteins. (B) Exon–intron organization of StbHLH genes. Red boxes represent exons and black lines of the same length represent introns. The upstream and downstream regions of StbHLH genes are indicated by green boxes. The numbers 0, 1 and 2 represent the intron phases. The sizes of exons can be estimated by the scale at bottom. (C) Arrangements of conserved motifs in the StbHLH proteins. Twenty predicted motifs are represented by different colored boxes, and motif sizes are indicated by the scale at bottom. For motif details refer to . CDS: coding sequence.