Overexpression of Malus baccata WRKY40 (MbWRKY40) enhances stress tolerance in Arabidopsis subjected to cold and drought

Abstract

The Malus baccata (L.) Borkh is a species of apple in the Rosaceae family, which grows in northern China and has excellent drought and cold resistance. It is an excellent apple rootstock for obtaining well-resistant apple varieties and has certain economic value. WRKY-TFs act as regulators in response to abiotic stress, so it is necessary to research the function of WRKY gene in Malus baccata in order to study whether the resistance of Malus baccata is related to WRKY TFs. The MbWRKY40 was isolated for the first time. Through qRT-PCR analysis, it was found that there were differences of MbWRKY40 in all organs of plants. At the same time, its expression increased rapidly under multiple stresses, but was higher under cold and drought stresses. The response mechanism of MbWRKY40 under cold and drought stresses was analyzed through genetic transformation and qRT-PCR research methods, and the relevant physiological indicators of transgenic Arabidopsis were measured. Using GraphPad Prism software to analyze the measured data, it was found that transgenic plants with heterologous expression of MbWRKY40 showed improved tolerance to stress. Transgenic plants had higher chlorophyll and proline contents, but lower malondialdehyde (MDA) content and electrolyte leakage rate (EL). Overexpression of MbWRKY40 can also effectively scavenge reactive oxygen species by positively regulating anti-oxidant enzymes activities under stress treatments. Meanwhile, the high expression of MbWRKY40 promoted the accumulation of AtKIN1, AtDREB2A, AtRD29A, AtERD10, AtCOR47A, and AtRD29B genes in Arabidopsis. Based on these data, it can be inferred that this gene may up-regulate downstream stress-related genes through ABA-induced pathways, thereby improving the survival ability of transgenic plants. The results not only enrich the progress of WRKY TFs in Malus baccata in abiotic stress, but also provide a new possibility for molecular breeding of apple resistance.