MdHAL3, a 4'-phosphopantothenoylcysteine decarboxylase, is involved in the salt tolerance of autotetraploid apple.

key messageMdHAL3 has PPCDC activity and is involved in the salt tolerance of autotetraploid apple. Apple (Malus × domestica) is the most widely planted fruit tree species worldwide. However, the growth and development of apple have been increasingly affected by abiotic stress, such as high salinity. In our previous study, RNA sequencing (RNA-seq) analysis revealed that the expression level of the MdHAL3 gene was significantly upregulated in the autotetraploid apple cultivar Hanfu. In the present study, we first isolated HAL3, whose product was shown to exert 4'-phosphopantothenoylcysteine decarboxylase (PPCDC) activity, from apple. MdHAL3 was expressed in all organs of apple, and its expression was rapidly induced by salt stress. The MdHAL3 protein was localized to the cytomembrane and cytoplasm. Five MdHAL3 overexpression (OE) lines and five MdHAL3-RNAi apple lines were obtained. We found that MdHAL3 enhanced the salt stress tolerance of apple and that the OE plants rooted more easily than the wild-type (WT) plants. The coenzyme A (CoA) content in the leaves of the OE plants was greater than that in the leaves of the WT plants, and the CoA content in the MdHAL3-RNAi plants was lower than that in the WT plants. Taken together, our findings indicate that MdHAL3 plays an essential role in the response to salt stress in apple.