Analysis of Herbivore Stress- and Phytohormone-Mediated Urease Expression in Soybean (Glycine max)
Ureases catalyze the hydrolysis of urea into ammonia and carbon dioxide and, thus, are involved in the metabolism and bioavailability of nitrogen. Ureases occur in plants, fungi, and bacteria. In plants, besides their enzymatic activity, ureases as proteins play a role in defense against insect and phytopathogenic fungi. Little is known about the regulation of urease in plants under stress and whether or not phytohormones may be involved. In this study, we addressed the regulation of ubiquitous urease (ubSBU) gene expression after phytohormone applications, insect herbivory, and mechanical damage in soybean (Glycine max cv. Williams 82). Stress-related phytohormones were applied. In addition, Spodoptera littoralis feeding and mechanical damage by MecWorm were performed. Ureolytic activity and transcripts for ubSBU and UreG were quantified. Roots and leaves showed the highest levels of ubSBU transcripts. The results show a significant increase of ubSBU transcripts upon jasmonic acid application and after herbivory, but downregulation after MecWorm treatment. UreG transcripts were downregulated after MecWorm, S. littoralis, and application of gibberellic acid, but upregulated by jasmonic acid. However, the ureolytic activities in leaves were influenced neither by phytohormones nor by herbivory and MecWorm. We conclude that the enzymatic activity of ureases is constitutive and basal levels of the enzyme are sufficient to perform the ureolytic activities in defense against insects and fungi. The defense role of ureases, which does not require the ureolytic activity, may underlie their differential regulation in response to different stress stimuli.
KeywordsSoybean Urease Phytohormones Herbivory Gene expression
We thank the greenhouse team at the MPI for Chemical Ecology for growing soybean plants and Angelika Berg for rearing caterpillars. We further thank Todd G. Bedford, USDA/ARS, Urbana, Illinois, for kindly providing soybean seeds and Wilhelm Boland and the Max Planck Society for continuous support. This work was further supported in part by the German Academic Exchange Service (DAAD; PPP Project ID 57142556) (AM), by the Brazilian agency Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Program PROBRAL 28/2014, Grant 6097-14-6 (ABBR, AM, CRC, RSS). ABBR and RSS also thank ULBRA and IFSul for the support. The authors are grateful to Thomas E. Burks for language editing.
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