Effect of long-term storage on the change in the expression of selected Mal d 1 gene isoforms in the apple cultivar Opal

Apples are available all year round since they can be stored for long time. However, the expression of the major apple allergen Mal d 1 can increase in the fruit during storage and incease so the risk of allergies in sensitive consumers. Therefore, we studied the change in the expression of the Mal d 1 gene during storage in the modern cultivar UEB 32642 (known under the brand name Opal (R)) and the cultivar Gala Brookfield (cv. Gala) as a reference. The cultivars were stored under two different conditions, ultra-low oxygen (ULO) and standard cold conditions. The gene expression was evaluated both in fresh fruits and in fruits stored for four, six, and nine months. Nine isoforms of the gene Mal d 1 with the highest published expression were quantified using real-time PCR. The most expressed isoforms Mal d 1.01, Mal d 1.02 and Mal d 1.06A were found in the fresh and also in the stored fruits. The expression of the Mal d 1.03G and Mal d 1.06D isoforms was higher the sored fruits. Our study confirmed that (i) Opal (R) had a lower overall expression of the Mal d 1 gene than cv. Gala, both in the fresh and stored fruits; (ii) standard cold storage is superior in preserving lower Mal d 1 levels in Opal (R) apples compared to the ULO conditions; and (iii) less expressed isoforms may be responsible for the general increase in the Mal d 1 gene expression during storage.