Abstract
BackgroundCassava plants (Manihot esculenta Crantz) have obvious abscission zone (AZ) structures in their leaf pulvinus-petioles. Cassava leaf abscission can be triggered by either 17 days of water-deficit stress or 4 days of ethylene treatment. To date, little is known about cassava AP2/ERF factors, and less is known regarding their roles in regulating abscission zone development.ResultsHere, the cassava and Arabidopsis AP2/ERF genes were compared, finding that the cassava genome contains approximately 1.54-fold more ERF subfamily than the Arabidopsis genome. Microarray analysis was used to identify the AP2/ERF genes that are expressed in cassava leaf pulvinus-petiole abscission zones by comparing the AP2/ERF gene expression profiles of ethylene- and water-deficit stress-induced leaf abscission. In total, 99 AP2/ERF genes were identified as 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 at six time points during ethylene- and water-deficit stress-induced leaf abscission demonstrated that 20 ERF subfamily genes had similar expression patterns in response to both treatments. GO (Gene Ontology) annotation confirmed that all 20 ERF subfamily genes participate in ethylene-mediated signalling. Analysis of the putative ERF promoter regions shown that the genes contained primarily ethylene- and stress-related cis-elements. Further analysis of ACC oxidase activity in AZs across six time points during abscission shown increased ethylene production in response to both ethylene and water-deficit stress; however, the difference was more dramatic for water-deficit stress. Finally, the expression ratios of 20 ERF subfamily genes were analysed in two cassava cultivars, ‘KU50’ and ‘SC5’, that exhibit different levels of leaf abscission when challenged with the same water-deficit stress. The analysis indicated that most of the ERF genes were expressed at higher levels in the precocious abscission ‘KU50’ cultivar than in the delayed abscission ‘SC5’ cultivar.ConclusionCcomparative analysis of both ethylene- and water-deficit stress-induced leaf abscission shown that the ERF subfamily functions in the regulation of cassava abscission zone development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2845-5) contains supplementary material, which is available to authorized users.
Highlights
Cassava plants (Manihot esculenta Crantz) have obvious abscission zone (AZ) structures in their leaf pulvinus-petioles
Comparative analysis of apetala2/ethylene response factor (AP2/ethylene-responsive factor domain (ERF)) gene expression profiles during ethylene- and waterdeficit stress-induced leaf abscission resulted in the selection of 24 AP2/ERF genes distributed among the different time points, including 20 ERF subfamily genes, 3 DERB subfamily genes, and one RAV subfamily gene (Additional file 5: Table S5), suggesting that ERF subfamily genes play important roles in cassava abscission zone development
Comparative analysis of transcriptome expression profiles in response to ethylene and water-deficit stress indicated that most AP2/ERF genes were expressed in response to both treatments, suggested that the same AP2/ERF genes may function in leaf abscission in response to different treatments
Summary
Cassava plants (Manihot esculenta Crantz) have obvious abscission zone (AZ) structures in their leaf pulvinus-petioles. Little is known about cassava AP2/ERF factors, and less is known regarding their roles in regulating abscission zone development. In Arabidopsis, 145 AP2/ERF genes have been characterized and are divided among five families [6]: those containing two AP2 domains (AP2), one AP2 domain and an ethylene-responsive factor domain (ERF), one AP2 domain and a dehydration-responsive elementbinding protein domain (DREB), one AP2 domain and one B3 domain (RAV), and the Soloists [5]. The AP2/ERF family is known to have important functions in plant growth and development, as well as in abiotic and biotic stress responses [13]. The ERF subfamily has specific functions in the regulation of abscission zone development [14, 16] and biotic stress response [5]. SHA1 and FUF1 both function in AZ development, whereas the two tomato genes function in AZ breakdown
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