Researchers Uncover Molecular Defenses in Cold-Resilient Loquat

Loquat (Eriobotrya japonica) is an evergreen fruit tree whose winter growth and flowering make it especially vulnerable to sudden freezes. When temperatures fall below zero, membranes lose flexibility, chloroplasts deteriorate, electron transport slows, and photosynthesis may collapse. Polyploid breeding has already produced loquats with seedless fruit, strong growth, and improved environmental adaptability, but the mechanisms behind their cold resistance remain poorly defined. Unsaturated membrane lipids are known to protect plants at low temperatures, yet it has been unclear which lipids matter most in triploid loquat or how their production is regulated. Based on these challenges, there is a need to investigate how polyploid loquat protects its photosynthetic machinery during freezing stress.

A research team based primarily at Southwest University, with participation from Huazhong Agricultural University, published (DOI: 10.1093/hr/uhag096) the study on March 16, 2026, in Horticulture Research. Most authors were affiliated with Southwest University's horticulture college and two agricultural and ecological research laboratories. The researchers compared diploid, triploid, and tetraploid loquat plants and combined freezing treatments with physiological measurements, membrane imaging, lipid profiling, transcriptome analysis, and gene-function tests. Their findings show that triploid plants maintain photosynthesis by increasing membrane-lipid unsaturation and identify a pathway in which the EjMYBS3 transcription factor activates EjFAD2, promoting protective phosphatidylcholine (PC) 18:2/18:2.

The team first exposed plants of three ploidy levels to temperatures ranging from 0°C to −15°C. At −3°C, only the triploid loquats maintained a positive net photosynthetic rate, and they had the lowest estimated semilethal temperature, −13.35°C. Transmission electron microscopy (TEM) showed that triploid chloroplast membranes remained clearly defined at −3°C, while diploid chloroplasts displayed extensive membrane fusion. Recovery tests reinforced this advantage: after −5°C treatment, triploid and tetraploid plants had survival rates of 50% and 25%, respectively, whereas all diploids died.

Liquid chromatography–tandem mass spectrometry (LC–MS/MS) detected 5,683 significantly altered lipids in triploids, compared with 743 in diploids and 1,788 in tetraploids. Phosphatidylcholine showed the strongest triploid-specific response, with PC 18:2/18:2 rising consistently across three independent triploid lines. Quantitative gene-expression tests confirmed that EjFAD2 was especially responsive to freezing in all three lines. Expressing EjFAD2 in Arabidopsis thaliana reduced electrolyte leakage and lipid peroxidation, preserved photosystem II (PSII) activity, and supported healthier recovery after cold exposure. Promoter-binding experiments then showed that the EjMYBS3 transcription factor directly activates EjFAD2. Finally, transient expression of either EjFAD2 or EjMYBS3 in loquat increased PC 18:2/18:2, strengthened photosynthetic performance, and improved freezing tolerance.

The authors said the triploid advantage is not simply a matter of carrying an extra chromosome set; it is expressed through a coordinated biochemical response that keeps membranes functional as temperatures fall. They said PC 18:2/18:2 appears to act as a central protective component, helping chloroplasts retain structure and sustain photosynthetic electron transport. The authors added that identifying EjMYBS3 as a regulator of EjFAD2 turns a broad polyploid trait into a defined molecular pathway, making it possible to test specific markers and breeding strategies rather than relying only on visible cold-tolerance traits.

These findings suggest two complementary routes for improving loquat production. Breeders could use triploid germplasm to combine seedlessness, vigorous growth, and greater freezing tolerance, while EjFAD2, EjMYBS3, and PC 18:2/18:2 could serve as candidate markers for selecting cold-resilient lines. The pathway may also help researchers examine whether similar lipid-based defenses operate in other polyploid fruit crops. In practical terms, stronger freezing tolerance could reduce orchard losses, stabilize yields during increasingly erratic winters, and potentially expand loquat cultivation into cooler regions. However, the results come mainly from controlled freezing experiments and short-term functional tests, so multi-year field evaluations will be needed before the pathway can be translated into commercial cultivars.