Transcriptomic and physiological analyses revealed the effects of exogenous MeJA on the antioxidant system and hormone signaling network in apple roots (Malus baccata L.) in response to suboptimal low root-zone temperature stress

Abstract

Low temperature limits the growth and yield of apple trees. Previous experiments have proven that exogenous methyl jasmonate (MeJA) can improve the low-temperature adaptability in Malus baccata Borkh. roots which is widely used as rootstocks in northern China. Whereas the molecular mechanism of MeJA regulating the suboptimal low-temperature adaptability of apple roots remain poorly understood. The purpose of this work was to explore the potential regulating mechanisms of jasmonate signal in M. baccata roots in response to suboptimal low root-zone temperature stress (5 ± 0.5 °C for 2 h) through transcriptome and physiological analysis. Transcriptome bioinformatics analyses demonstrated that 2285 differentially expressed genes (DEGs) were predominantly associated with the jasmonates biosynthesis, hormone signaling pathways, MAPK signaling, and glutathione metabolism. Further investigations highlighted the regulating role of JAs in the low-temperature acclimation of the apple roots. Firstly, MeJA application inhibited the accumulations of reactive oxygen species and malondialdehyde in M. baccata roots through increasing antioxidant enzyme activities under suboptimal low-temperature, together with the increase of endogenous JAs levels. Secondly, the transcriptional levels of several pivotal JAs signaling genes were significantly up-regulated in the MeJA pre-treated roots under suboptimal low-temperature, verified through expression profiling and qRT-PCR analyses. Thirdly, MbMYC2 directly bound to the promoter of MbPOD, encoding a transcription factor involved in the antioxidant system, and enhanced its transcription. In summary, the mechanism of MeJA enhancing the antioxidant adaptability of M. baccata roots under suboptimal low-temperature stress has been preliminarily clarified, which provides new insights for further elaboration of molecular mechanism that are involved in low-temperature adaptability of apple roots.