AtMYB20 is negatively involved in plant adaptive response to drought stress

MYB transcription factors play critical roles in plant development and stress responses. Our objective was to characterize a role of AtMYB20 (AT1G66230) in regulating the ABA-dependent adaptive response to desiccation stress in Arabidopsis. Sequencing analysis revealed that there is a site located on the AtMYB20 transcript which is potentially base-paired by miR858. To avoid the possible cleavage, a vector with a miR858-resistant version of AtMYB20 under the CaMV 35S promoter (35S:m5AtMYB20) was constructed. The AtMYB20 knock-out mutant myb20 was applied to identifying AtMYB20 functions. While AtMYB20 was induced by high levels of NaCl, its expression was suppressed by desiccation and cold stresses and abscisic acid (ABA) treatment. Compared with wild-type, AtMYB20 over-expression (35S:m5AtMYB20) seedlings were susceptible to desiccation, whereas MYB20 loss of function mutant myb20 plants displayed resistance to desiccation stress. 35S:m5AtMYB20 plants were less sensitive to ABA, but myb20 mutants were hypersensitive to ABA. This could be validated by the experiment in which treatment with 10 mu M ABA for 2 h resulted in constant stomatal opening on leaves of 35S:m5AtMYB20 plants but stomatal closure on myb20 mutant plants. Expression of ABA- and drought stress-responsive marker genes (e.g. ABI3-5 and ABF3-4) was up-regulated in myb20 plants but down-regulated in 35S:m5AtMYB20 plants. AtMYB20 acts as a negative regulator of plant response to desiccation stress in an ABA-dependent manner.