Overexpression of the Pyrus sinkiangensis LEA4 Gene Enhances the Tolerance of Broussonetia papyrifera to the Low Temperature During Overwintering

Korla fragrant pear (<i>Pyrus sinkiangensis</i>), valued for its unique flavor, suffers from freezing damage in its native Xinjiang. Previous studies indicated a strong correlation between low-temperature stress and the expression of LEA genes, particularly <i>PsLEA4</i>. This study cloned <i>PsLEA4</i> from <i>P. sinkiangensis</i> and overexpressed it in paper mulberry (<i>Broussonetia papyrifera</i>). The encoded 368-amino-acid protein is localized to the endoplasmic reticulum. Under -4 °C stress, the proline and soluble protein contents in the overexpressing lines increased to 1.21-fold and 1.36-fold, respectively, compared to the wild type, while relative water content (RWC) reached 1.58-fold. And catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities increased by 9%, 16%, and 38%, respectively. During overwintering, the transgenic line exhibited soluble protein content and RWC at 1.78-fold and 1.49-fold compared to those of the wild type, respectively. Malondialdehyde (MDA) and relative electrolyte leakage (REL) levels were only 66% and 63% of the wild type, while CAT and POD activities reached 1.87-fold, and SOD activity peaked at 2.49-fold. These adaptations were associated with improved cold tolerance and with bud break occurring 7-10 days earlier than in WT the following year. These findings could help to understand the molecular mechanisms of <i>P. sinkiangensis</i> for overwintering and provide new genetic resources to breed varieties of pear that can resist cold temperatures.