Tomato PERK gene family revealed through genome-wide stress expression analysis

Scientists have completed the first systematic, genome-wide inventory of a family of stress-sensing genes in tomato, revealing that just six genes—each encoding a molecular antenna on the cell surface—may hold some of the secrets to how one of the world’s most important vegetable crops copes with cold, heat and salty soils. The study, published in the journal 3 Biotech, charts the proline-rich extensin-like receptor kinase, or PERK, gene family in tomato (Solanum lycopersicum) using the most up-to-date reference genome available, and then follows the activity of these genes through controlled stress experiments on two contrasting tomato cultivars. The results point to a striking difference between varieties: one cultivar, GMOTL-1, switched on its PERK genes far more vigorously and broadly under stress than the widely grown Roma variety, hinting that these genes could underpin cultivar-specific stress tolerance and could become targets for breeding climate-resilient tomatoes.

PERK genes belong to the vast superfamily of receptor-like kinases, the molecular sentinels that stud plant cell membranes and translate external signals into internal biochemical commands. A typical PERK protein is a modular device: an extracellular region rich in proline and reminiscent of extensin—a structural cell-wall protein—sits outside the membrane, linked through a single membrane-spanning segment to an intracellular serine/threonine protein kinase domain. When an appropriate cue is perceived at the cell surface, the kinase domain can become activated through phosphorylation, launching cascades of downstream signalling. Previous work in other species had already linked PERK proteins to important processes: the Arabidopsis PERK4 protein, for example, was shown to regulate calcium signalling and abscisic acid responses, while PERK1 in bean is rapidly induced by wounding. Genome-wide analyses in crops such as wheat, cotton, maize and Brassica rapa have likewise suggested roles in development and environmental response. Tomato, however, had remained comparatively unexplored for this family until now.

The research team worked from the SL4.0/ITAG4.0 genome assembly, the latest and most refined annotation of the tomato genome, to locate and verify every member of the PERK family. Their search yielded six genes, designated SlPERK1 through SlPERK6, and every one of them was confirmed to carry the conserved serine/threonine protein kinase domain that defines the family’s catalytic function. The modest size of the family compared with the expansions seen in some polyploid crops makes tomato an unusually clean system for dissecting what each gene does, since redundancy among close relatives is limited.

To understand how these six genes had evolved, the researchers performed phylogenetic and structural comparisons. One of the most informative measures in evolutionary genetics is the ratio of non-synonymous to synonymous substitution rates, known as Ka/Ks. Non-synonymous substitutions change the amino acid sequence of a protein, while synonymous substitutions do not, so a Ka/Ks value below 1 indicates purifying selection—evolutionary pressure to preserve the protein sequence because changes are typically harmful. In the case of the SlPERK genes, Ka/Ks values were consistently below 1, indicating strong purifying selection and suggesting that the functions of these kinases are so important to the plant that damaging mutations are weeded out over generations. The team also examined exon-intron architecture, the pattern of coding regions and intervening non-coding sequences within each gene, and found distinct organizational differences among family members—a feature often associated with functional divergence, where genes that arose from a common ancestor have taken on specialized roles.

Because gene activity is regulated not only by the gene itself but by the DNA elements that control it, the researchers scanned the promoter regions upstream of each SlPERK gene for cis-regulatory elements—short DNA motifs that serve as binding sites for transcription factors. Their analysis uncovered an abundance of stress-responsive and hormone-responsive elements, including motifs associated with responses to abscisic acid, drought, cold and salinity. This finding is significant because it suggests the genes are wired at the regulatory level to respond to exactly the kinds of environmental challenges the researchers would go on to test experimentally. In effect, the promoters of the SlPERK genes carry built-in switches tuned to adverse conditions.

The team went a step further by exploring regulation after transcription. Using computational prediction, they identified 57 microRNAs—small regulatory RNAs that can bind complementary sequences in messenger RNAs and either cleave them or block their translation—as potential post-transcriptional regulators of the SlPERK genes. They also constructed protein-protein interaction networks, revealing that the PERK proteins are predicted to connect with a broader web of signalling components. Together, these analyses sketch a picture of a small gene family embedded in multiple layers of control, from transcriptional regulation through microRNA-mediated tuning to network-level interactions with other signalling proteins.

Bioinformatics alone, however convincing, cannot establish a role in stress tolerance, so the researchers validated their predictions in the greenhouse. They selected two tomato cultivars with different genetic backgrounds—GMOTL-1 and Roma—and exposed them to three abiotic stresses: cold, heat and salinity. They then measured gene expression using quantitative reverse-transcription PCR, a laboratory technique that converts messenger RNA into complementary DNA and amplifies it to quantify how active each gene is under different conditions. Expression levels were normalized using established relative-quantification methods, allowing precise comparison of gene activity between stressed and unstressed plants and between the two cultivars.

The qRT-PCR results revealed cultivar-specific expression dynamics that matched the computational predictions in compelling ways. SlPERK4 showed strong transient induction under cold and heat stress, meaning its activity spiked rapidly in response to temperature extremes before subsiding—a pattern typical of genes involved in early stress signalling rather than long-term physiological adjustment. SlPERK6, by contrast, proved highly responsive to salinity, its expression climbing when plants were grown under salt treatment. Perhaps most striking was the difference between the cultivars. GMOTL-1 displayed significantly higher and broader stress-responsive expression across the SlPERK family than Roma, its genes responding more strongly and to a wider range of stresses. This pattern suggests that the more robust expression of PERK-mediated signalling could contribute to the superior stress tolerance observed in some tomato backgrounds, and it provides breeders with a molecular signature they might look for when screening germplasm for resilient lines.

The implications extend well beyond basic biology. Tomatoes are grown on every continent and are a cornerstone of global diets, yet they are notoriously sensitive to environmental extremes. Cold snaps damage membranes and photosynthetic machinery, heat waves impair pollen development and fruit set, and soil salinity—exacerbated by irrigation and climate change—suppresses growth and yield across millions of hectares. Conventional breeding for stress tolerance is slow, and the underlying genetics is often complex. Genomic resources like the one assembled here accelerate that process by pinpointing candidate genes whose regulation or sequence could be targeted by marker-assisted selection or, increasingly, by gene-editing tools such as CRISPR-Cas9, which has already been applied to enhance abiotic stress resilience in tomato. A compact, well-characterized gene family with clear stress-responsive members is precisely the kind of resource that functional validation and molecular breeding programmes need.

The study, supported by an ALP-funded project of the Pakistan Agricultural Research Council, also reflects the growing power of combining the newest genome assemblies with classical stress physiology. By anchoring their search in SL4.0/ITAG4.0, the researchers minimized the risk of missing genes or misannotating family members—an issue that has plagued earlier family-wide studies built on older assemblies. By pairing bioinformatics with experimental expression profiling in two cultivars, they moved from prediction to evidence, demonstrating that the SlPERK genes are not merely present in the genome but actively engaged in the plant’s response to its environment. As climate variability intensifies, understanding how sensor genes like PERKs tune a crop’s response to adverse conditions will become increasingly important. For now, the six SlPERK genes stand as both a genomic resource and a set of molecular leads: SlPERK4 for temperature stress, SlPERK6 for salinity, and the cultivar contrast between GMOTL-1 and Roma as a roadmap for breeding tomatoes that can thrive in a warming, salinizing world.