Abstract
Cassava plants (Manihot esculenta Crantz) resist environmental stresses by shedding leaves in leaf pulvinus abscission zones (AZs), thus leading to adaptation to new environmental conditions. Little is known about the roles of cassava R2R3 MYB factors in regulating AZ separation. Herein, 166 cassava R2R3 MYB genes were identified. Evolutionary analysis indicated that the 166 R2R3 MYB genes could be divided into 11 subfamilies. Transcriptome analysis indicated that 26 R2R3 MYB genes were expressed in AZs across six time points during both ethylene- and water-deficit stress-induced leaf abscission. Comparative expression profile analysis of similar SOTA (Self Organizing Tree Algorithm) clusters demonstrated that 10 R2R3 MYB genes had similar expression patterns at six time points in response to both treatments. GO (Gene Ontology) annotation confirmed that all 10 R2R3 MYB genes participated in the responses to stress and ethylene and auxin stimuli. Analysis of the putative 10 R2R3 MYB promoter regions showed that those genes primarily contained ethylene- and stress-related cis-elements. The expression profiles of the genes acting downstream of the selected MYBs were confirmed to be involved in cassava abscission zone separation. All these results indicated that R2R3 MYB plays an important regulatory role in AZ separation.
Highlights
The Arabidopsis genome contains 126 R2R3 MYB genes[2,3]
TaMYB4 from wheat is induced by salicylic acid, ethylene, abscisic acid and methyl jasmonate hormones, and it enhances the response to different stresses and promotes disease resistance[15]
All cassava MYB proteins were manually inspected to ensure that the putative genes contained 2 or 3 MYB repeats
Summary
The Arabidopsis genome contains 126 R2R3 MYB genes[2,3]. Many R2R3 MYB genes are involved in regulating environmental stress responses, ROS signaling pathways, and hormone signaling pathways. By using transcriptomic, physiological, cellular, molecular, metabolic and transgenic methods, we have found that ROS and ethylene regulate the separation of abscission zones under water-deficit stress. Transcriptome analysis was used to identify the R2R3 MYB genes expressed in cassava leaf pulvinus-petiole abscission zones by comparing the R2R3 MYB gene expression profiles of ethylene- and water-deficit stress-induced leaf abscission. 41 and 38 R2R3 MYB genes were expressed during ethylene- and water-deficit stress-induced leaf abscission, respectively. 26 R2R3 MYB genes were identified as being expressed in AZs across six time points during both ethyleneand water-deficit stress-induced leaf abscissions. Comparative expression profile analysis of similar SOTA (Self Organizing Tree Algorithm) clusters at six time points during ethylene- and water-deficit stress-induced leaf abscission demonstrated that 10 R2R3 MYB subfamily genes exhibited similar expression patterns in response to both treatments. Our results should be useful for determining the precise role of R2R3 MYB genes participating in the process of cassava abscission zone separation
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