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Figure 1. 

(a) Distribution and (b) duplication of SlKRP genes on tomato chromosomes. Chromosome numbers are indicated at the top of each bar.

Figure 2. 

Gene structures and conserved domains of SlKRP genes. (a) Exon-intron structure of the SlKRP genes. (b) Distributions of conserved motifs in SlKRP proteins. The 1−20 motifs in SlKRP proteins were identified by the MEME program (http://meme-suite.org/), which were displayed by different colored boxes. Motif 1 is cyclin-dependent kinase inhibitor domain.

Figure 3. 

Phylogenetic trees showing KRP genes from tomato, tobacco, Arabidopsis, capsicum and eggplant. The KRP proteins were classified into three subfamilies and distinguished by different colors.

Figure 4. 

Expression characterization of SlKRP genes. (a) Expression profiles of SlKRP genes in different tissues, including root, stem, leaf, flower, anthesis, immature green fruit (IMG), mature green fruit (MG), breaker fruit (BR), yellow fruit (YR), and red ripe fruit (RR). The expression levels of SlKRP genes were calculated using the CT method. Data shown are means ± SD (n = 3). The β-actin gene was used as an internal control. (b) Subcellular localization of SlKRP-GFP (green fluorescent protein) fusion proteins in tobacco leaf epidermal cells. The nuclei were determined by DAPI staining.

Figure 5. 

Cis-regulatory elements in the promoter regions of SlKRP genes.

Figure 6. 

Expression profiles of SlKRP genes under various environmental stressors and phytohormone treatment. Expression profiles of SlKRP genes in tomato plants after (a) salt , (b) drought, and (c) low temperature treatments. The β-actin gene was used as an internal control. The data are presented as the means ± SDs (n = 3). The different letters indicate statistically significant differences at a 5% level of significance according to Tukey's pairwise comparison tests. A heatmap displaying SlKRP genes expression under (d) light, (e) ABA, IAA and (f) ACC treatments. Red and blue represented up-regulated and down-regulated gene expression after treatment, respectively.

Figure 7. 

Co-expression analysis of SlKRP, SlCDK and cyclin genes in tomato. The color of the circles indicates the correlation coefficient value of gene co-expression in the R environment.

Figure 8. 

The predicted protein interaction network of the SlKRP proteins in tomato using string database.

Figure 9. 

Knockdown of SlKRP5 reduces drought stress tolerance in tomato. (a) Phenotype of SlPDS-silenced tomato plant via VIGS. (b) Expression level of SlKRP5 in SlKRP5-silenced and control plants. (c) Phenotype of SlKRP5-silenced and control plants treated with PEG6000 (25% w/v). Scale bar, 3 cm. DAB staining for (d) H₂O₂ and (e) NBT staining for superoxide in control and SlKRP5-silenced tomato leaves. (f) MDA content, (g) SOD activity and (h) POD activity in SlKRP5-silenced and control plants. The data are presented as the means ± SDs (n = 3). The different letters indicate statistically significant differences at a 5% level of significance according to Tukey's pairwise comparison tests.