Whole genome identification and analysis of cotton(Gossypium hirsutum L.) pyruvate kinase gene family and functional analysis of GhPK5 gene

Plants are constantly balancing a delicate ledger of energy. To grow, to reproduce, and to survive the harshness of a dry or salty day, they must break down sugars into usable power. One of the most critical steps in this process is a chemical reaction that turns a sugar intermediate into pyruvate, a molecule that fuels the cell's engines. The enzyme that drives this specific step is called pyruvate kinase. It acts as a gatekeeper, controlling the flow of energy. While scientists have studied this enzyme in model plants like rice and mustard weed for decades, the cotton plant has remained a bit of a mystery in this regard. Cotton is a global economic powerhouse, providing the fiber for much of the world's clothing, yet its ability to withstand the salt and drought that often plague its fields is a major bottleneck for farmers. Understanding how cotton manages its energy under pressure could hold the key to growing stronger, more resilient crops.

A team of researchers at Zhejiang Sci-Tech University set out to map the entire family of pyruvate kinase genes in upland cotton, the most widely grown variety of the crop. They began by scanning the cotton genome, the complete set of genetic instructions, to find every gene that codes for this vital enzyme. They discovered forty-one distinct genes, a surprisingly large number compared to other plants. By comparing the genetic sequences of these genes to those in rice and Arabidopsis, the researchers sorted them into two main groups: one group that operates in the cell's fluid interior and another that works inside the plant's chloroplasts, the solar-powered factories where photosynthesis occurs. The team then traced where these genes sit on the cotton chromosomes. They found the genes scattered across nineteen different chromosomes, with some areas crowded with multiple copies while others were empty. The pattern suggested that the family grew primarily through a process where large chunks of the genome were copied and pasted, rather than through small, random mutations.

The researchers also looked at the internal architecture of these genes, examining how their coding sections were arranged and what specific protein building blocks they contained. They found that genes within the same group shared very similar structures, suggesting they perform related tasks. To understand what might turn these genes on or off, the team examined the DNA sequences just before the genes start, looking for regulatory switches. They found a rich collection of these switches, many of which are known to respond to environmental stressors like cold, drought, and salt, as well as to plant hormones. This indicated that the cotton plant has a sophisticated system for adjusting its energy production when the weather turns bad.

To see how these genes actually behave in a living plant, the scientists analyzed data from cotton growing in different parts of the plant, from roots to flowers. They found that while some genes were active only in specific tissues, one gene in particular, named GhPK5, was a standout. It was active at high levels in almost every part of the plant, from the roots deep in the soil to the stems and leaves. When the researchers subjected the plants to salt stress, drought, heat, and cold, GhPK5 responded with a strong and sustained increase in activity, especially under salt and drought conditions. This pattern suggested that GhPK5 was not just a background worker but a central player in the plant's defense against harsh environments.

To confirm this role, the team performed a direct test using a technique that temporarily silences the gene, effectively turning it off to see what happens. They created cotton plants where GhPK5 was silenced and then exposed them to salty water. The results were clear: without GhPK5, the plants suffered significantly more damage. Their cells accumulated higher levels of harmful byproducts that indicate oxidative stress, and their ability to produce pyruvate, the essential fuel molecule, was impaired. In contrast, the normal plants with the active gene were able to maintain their energy levels and protect their cells from damage. This experiment proved that GhPK5 acts as a positive regulator, helping the plant fight off the effects of salt.

The study concludes that the cotton pyruvate kinase family is diverse and complex, with forty-one members working together to manage the plant's energy. Among them, GhPK5 emerges as a critical component for surviving salt stress. By keeping the energy flow steady and protecting the cell from damage, this gene helps the plant endure conditions that would otherwise be fatal. The findings provide a detailed map of how cotton manages its internal chemistry under pressure and highlight GhPK5 as a promising target for breeding programs. If scientists can enhance the activity of this gene, they may be able to develop cotton varieties that thrive in saline soils, securing the crop's future in an increasingly challenging climate.