Activation tagging identifies Arabidopsis transcription factor AtMYB68 for heat and drought tolerance at yield determining reproductive stages

Abstract

Heat stress occurring at reproductive stages can result in significant and permanent damage to crop yields. However, previous genetic studies in understanding heat stress response and signaling were performed mostly on seedling and plants at early vegetative stages. Here we identify, using a developmentally defined, gain-of-function genetic screen with approximately 18 000 Arabidopsis thaliana activation-tagged lines, a mutant that maintained productive seed set post-severe heat stress during flowering. Genome walking indicated this phenotype was caused by the insertion of 35S enhancers adjacent to a nuclear localized transcription factor AtMYB68. Subsequent overexpression analysis confirmed that AtMYB68 was responsible for the reproductive heat tolerance of the mutant. Furthermore, these transgenic Arabidopsis plants exhibited enhanced abscisic acid sensitivity at and post-germination, reduced transpirational water loss during a drought treatment, and enhanced seed yield under combined heat and drought stress during flowering. Ectopic expression of AtMYB68 in Brassica napus driven either by 35S or by heat-inducible promoter recapitulated the enhanced reproductive heat stress and drought tolerance phenotypes observed in the transgenic Arabidopsis. The improvement to heat stress is likely due to enhanced pollen viability observed in the transgenic plants. More importantly, the transgenic canola showed significant yield advantages over the non-transgenic controls in multiple locations, multiple season field trials under various drought and heat stress conditions. Together these results suggest that AtMYB68 regulate plant stress tolerance at the most important yield determining stage of plant development, and is an effective target for crop yield protection under current global climate volatility.

Genetic and Physiological Responses to Heat Stress in Brassica napus

“…At the physiological level, TFs also play important roles in plant growth and development. In A. thaliana , the ectopic expression of transcription factor AtMYB68 in B. napus following severe heat stress at flowering enhanced pollen viability and led to significant improvement in yield ( Deng et al, 2020 ). These findings show the key role of TFs in the reproductive heat tolerance system pertained by A. thaliana and other related species ( Yu et al, 2014 ) and altogether suggest a conserved stress response with key resistance factors in different tissues and plants ( Yu et al, 2014 ; Huang et al, 2019 ).…”

Gene Networks Involved in Plant Heat Stress Response and Tolerance

“…The survival rate of TaMYB80 -overexpressed seedlings following heat stress was significantly higher than that of the WT, indicating that TaMYB80 overexpression improved heat tolerance. In addition, under heat stress, compared with WT plants, AtMYB68 -overexpressed Arabidopsis exhibited increased sensitivity to ABA, reduced transpiration, and improved seed yield, showing that AtMYB68 overexpression improved the heat tolerance of Arabidopsis [ 87 ]. The overexpression of AtMYB68 controlled by the heat-inducible promoter P81.1 in Brassica napus also improved heat tolerance at the flowering stage, enhancing pollen viability and reducing water loss and transpiration under heat stress.…”

Adaptive protein evolution through length variation in short tandem repeats

“…The poly-E tract is in an intrinsically disordered region (IDR) approximately in the middle of the protein sequence. (3) Myb domain protein 68 is directly involved in toleration of severe heat stress ( 52 ). The poly-N tract is located after a larger IDR in the C-terminal half of the protein.…”