Cloning and Initial Functional Analysis of Abscisic Acid Receptor Gene MdPYL4 in Apple (Malus domestica)

INTRODUCTION: Abscisic acid (ABA), a phytohormone, plays crucial roles in multiple developmental and physiological processes throughout the plant life cycle. The ABA signaling pathway is essential for plant responses to both biotic and abiotic stresses. ABA receptor proteins, known as PYR/PYL/RCARs (PYLs), are key components of this pathway. Accumulating evidence demonstrates that PYL proteins modulate plant resistance to biotic stress. Therefore, identifying disease-resistance genes is crucial for the sustainable prevention and control of apple Glomerella leaf spot, a devastating disease that severely affects apple production. RATIONALE: To explore the biological function of the MdPYL4 gene, we cloned the gene, and investigated its subcellular localization and expression patterns under Colletotrichum gloeosporioides stress. RESULTS: Apple ABA receptor proteins (MdPYLs) respond to C. gloeosporioides infection. Phylogenetic analysis grouped MdPYLs into four subfamilies. MdPYL3 and MdPYL9, MdPYL11 and MdPYL4, and MdPYL6 and MdPYL13 are closely related and share conserved motifs. MdPYL4 clusters with PYL4 proteins from grape, melon, rice, and potato, and these proteins exhibit highly similar conserved motifs. In addition, the promoter regions of PYL4-clade genes contain cis-acting elements such as the W-box, TC-rich repeats, TCA-element, MYC, and MYB, which may be involved in plant stress responses and the regulation of metabolite biosynthesis, including alkaloids and flavonoids. MdPYL4 responded to plant-pathogen stress and localized to the cytoplasm and nucleus. STRING-based prediction suggested that MdPYL4 interacts with ABI2 and HAI3. MdPYL4 may participate in the MAPK cascade signaling pathway (MPK3/6) via HAI3 to regulate pathogen resistance. CONCLUSION: MdPYL4, an abscisic acid (ABA) receptor identified in apple, is predominantly localized in the cytoplasm and nucleus. Its expression is significantly affected by infection with Colletotrichum gloeosporioides. As a core component of the ABA signaling pathway, MdPYL4 is likely involved in phytohormone-mediated defense responses.