AtMYB44Enhances Disease Resistance And Heat Tolerance And Represses Flowering In Arabidopsis Thaliana

MYB transcription factors regulate the growth of plants and are also implicated in resistance against biotic stress and abiotic stresses, AtMYB44is a multifunction transcription factor, it is involved in a variety of plant growing stages. Including seed germination, the seeds maturing, and the resistance to pathogens, insects, and environmental stresses. In order to study the function of AtMYB44, the three genotypes Arabidopsis (wild-type Col-0, mutant atmyb44and overexpression plants MYB44OTA) are confronted with heat stress and the infection of Pseudomonas syringae pv. tomato DC3000(Pst DC3000). Meanwhile, its regulation to the flowering of Arabidopsis is also studied. The results showed that, AtMYB44enhance resistance of Arabidopsis to Pst DC3000by the salicylic acid signaling pathway; AtMYB44enhances the Arabidopsis thermal capacity by increasing the activities of antioxidant enzymes and transcriptional level of heat-resistant gene HSP; At the same time, as is showen in the study, AtMYB44delays flowering of Arabidopsis by alter the expression of several flowering regulation genes.1. AtMYB44positively modulates disease resistance to pseudomonas syringae DC3000through salicylic acid signaling pathway in ArabidopsisPrevious report shows that AtMYB44in Arabidopsis was dramatically induced by salicylic acid (SA) and biotrophic pathogen Pst DC3000infection. To understand the role of AtMYB44in defense responses, we analyzed both loss-of-function mutant atmyb44and AtMYB44over-expression (MYB44OTA) lines in response to Pst DC3000. The atmyb44mutant was more susceptible and the MYB44OTA lines were more resistant to Pst DC3000compared to the wild type. Moreover, blocking the SA synthesis or knocking out the NPR1gene suppressed the defense phenotype in the MYB44OTA plants. All these results indicate that AtMYB44mediates defense responses mainly through the SA signaling pathway. 2. AtMYB44negatively modulates flowering in Arabidopsis thalianaIn this study, the floral transition of the wild-type Col-0, loss-of-function mutant atmyb44and over-expression plant MYB44OTA was compared with each other under long-/short-day light irradiation and gibberellin treatment. In addition, the senescence marker gene SAG12was suppressed in the MYB44OTA over the atmyb44and Col-0plants. And, enhancement of activity of antioxidant enzyme (SOD, CAT and APX) was observed in the MYB44OTA over the Col-0or atmyb44plants. Molecular data indicates that the delayed floral transition is due to alterring the expression of several flowering regulation genes in the AtMFB44-overexpression plant. The expression levels of FT, SOC1and AGL24gene in overexpression plants was decreased and the expression of SVP and FLM was increased; Ho were, The expression levels of FT, SOC1and AGL24gene in mutant plants was increased and the expression of SVP and FLM was decreased. Yeast two-hybrid assays suggest that AtMYB44does not interact with FT, SOC1and CO. Based on the above evidences, we suggest that AtMYB44delays plant flowering.3. AtMYB44enhances heat tolerance in Arabidopsis thalianaIn this study, Three levels of temperature (25,35and45℃) treatment were applied on the wild-type Col-0, loss-of-function mutant atmyb44and over-expression MYB44OTA plants for two hours. Enhancement of heat tolerance was observed in MYB44OTA over these in Col-0under stress conditions. Higher H2O2accumulation and lipid peroxidation were measured in the Col-0, atmyb44in comparison to the MYB44OTA plants. And, enhancement of activities of antioxidant enzymes (SOD, CAT, APX and GR) was observed in the MYB44OTA plants over the Col-0or atmyb44plants under favorable or elevated growth conditions. Furthermore, higher expression of Hsp20,60,70,90and101genes was also monitored in the MYB44OTA over the Col-0and atmyb44plants. In the discussion, we consider that improvement of antioxidant capacity and HSP contributes to the enhancement of heat tolerance of the MYB44-overexpressed plant.