Myo-inositol mediates reactive oxygen species-induced programmed cell death via salicylic acid-dependent and ethylene-dependent pathways in apple

As a versatile compound, myo-inositol plays vital roles in plant biochemistry and physiology. We previously showed that exogenous application of myo-inositol had a positive role in salinity tolerance in Malus hupehensis Rehd. In this study, we used MdMIPS (the rate-limiting gene of myo-inositol biosynthesis) transgenic apple lines to gain new insights into the physiological role of myo-inositol in apple. Decreasing myo-inositol biosynthesis in apple lines by RNA silencing of MdMIPS1/2 led to extensive programmed cell death, which manifested as necrosis of both the leaves and roots and, ultimately, plant death. Necrosis was directly caused by the excessive accumulation of reactive oxygen species, which may be closely associated with the cell wall polysaccharide-mediated increase in salicylic acid and a compromised antioxidant system, and this process was enhanced by an increase in ethylene production. In addition, a high accumulation of sorbitol promoted necrosis. This synergetic interplay between salicylic acid and ethylene was further supported by the fact that increased myo-inositol accumulation significantly delayed leaf senescence in MdMIPS1-overexpressing apple lines. Taken together, our results indicated that apple myo-inositol regulates reactive oxygen species-induced programmed cell death through salicylic acid-dependent and ethylene-dependent pathways.