MhLHCA2 contributes to apple responses to iron deficiency by supporting photosynthetic performance and Fe-related physiological processes

Abstract Background Iron (Fe) is an essential micronutrient for plant growth and development. However, its bioavailability is extremely low in calcareous and alkaline soils, frequently resulting in Fe deficiency stress. Results In this study, MhLHCA2 was investigated using stable MhLHCA2 -overexpressing apple calli lines and virus-induced gene silencing in apple seedlings to assess its involvement in photosynthetic performance and Fe-deficiency responses. Fe deficiency reduced SOD, POD and CAT activities in all calli lines. However, under Fe deficiency, MhLHCA2 -overexpressing calli retained higher SOD and CAT activities than WT calli and accumulated lower levels of ROS and MDA. MhLHCA2 overexpression was also associated with higher FCR activity, Fe 2 ⁺ content, total Fe content, water-extractable total Fe content and expression of several Fe-deficiency-responsive genes. Conversely, transient MhLHCA2 silencing in apple seedlings was associated with impaired photosynthetic performance, increased PSI donor-side limitation and reduced photochemical efficiency under Fe-deficient conditions. These changes were accompanied by greater ROS accumulation, lower FCR activity, reduced tissue Fe contents and restricted root development. Conclusions Collectively, the complementary responses observed in stable MhLHCA2 -overexpressing apple calli and transiently silenced apple seedlings support the involvement of MhLHCA2 in photosynthetic performance, oxidative-stress responses and Fe-related physiological processes under controlled Fe-deficient conditions. However, these experimental systems do not replace stable whole-plant genetic validation. Regenerated stable overexpression and loss-of-function plants will be required to establish the long-term contribution of MhLHCA2 to whole-plant Fe-deficiency tolerance and Fe acquisition.