|RAO, S - University Of Kentucky|
|EL-HABBAK, M - University Of Kentucky|
|HAVENS, W - University Of Kentucky|
|SINGH, A - University Of Kentucky|
|ZHENG, D - University Of Illinois|
|VAUGHN, L - University Of Illinois|
|KORBAN, S - University Of Illinois|
|GHABRIAL, S - University Of Illinois|
Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2013
Publication Date: 10/7/2013
Publication URL: http://handle.nal.usda.gov/10113/62088
Citation: Rao, S.S., El-Habbak, M., Havens, W., Singh, A., Zheng, D., Vaughn, L., Haudenshield, J.S., Hartman, G.L., Korban, S., Ghabrial, S. 2013. Overexpression of GmCaM4 in soybean enhances resistance to pathogens and tolerance to salt stress. Molecular Plant Pathology. 15(2):145-160.
Interpretive Summary: Soybean is the major oilseed crop in the world and is a main source of oil and high-quality protein for both humans and animals worldwide. Plant diseases inflict heavy losses on soybean yield that negatively impact the US economy. Implicit in the high economic value of this crop is the importance of a comprehensive understanding of the molecular mechanisms underlying stress responses. Calcium is an element that serves as an important information carrier and is considered a universal messenger for conveying signals and regulating numerous aspects of plant responses to stresses. Calmodulins are calcium binding messenger proteins that deliver calcium in response to stress. In the present study, we used the bean pod mottle virus as a gene carrier to allow for the over-expression of calmodulins. Overexpression of calmodulins resulted in increased resistance to a root and stem rot pathogen, a leaf spot pathogen, and to a pod and stem pathogen indicating that overexpression provided additional plant protection to pathogens that infect various plant tissues. In addition, the overexpressing soybean plants exhibited increased tolerance to high salt conditions. Transgenic soybean plants with overexpression of calmodulins may provide added protection to the soybean crop under stressed conditions. This study is important to other plant molecular biologists and to the soybean industry interested in studies on understanding the role of host proteins in responses to abiotic and biotic stresses.
Technical Abstract: Soybean (Glycine max (L.) Merr.) is the major oilseed crop in the world and is a main source of oil and high-quality protein for both humans and animals worldwide. Plant diseases inflict heavy losses on soybean yield that negatively impact the US economy. Implicit in the high economic value of this crop is the importance of a comprehensive understanding of the molecular mechanisms underlying biotic/abiotic stress responses. Ca2+ is an important universal messenger for conveying signals and regulating numerous aspects of plant responses to stresses. Cellular changes in Ca2+ in response to diverse signals are recognized by protein sensors with calmodulins (CaMs) being the prominent Ca2+ sensors. In the present study, we used the bean pod mottle virus (BPMV)-based vector to explore the over-expression/silencing of SCaM4, a specific isoform of the soybean protein calmodulin. Overexpression of SCaM4 in soybean resulted in increased resistance to the root and stem rot pathogen Phytophthora sojae, the Alternaria leaf spot fungal pathogen Alternaria tenuissima, and to the pod and stem blight fungal pathogen Phomopsis longicolla. On the other hand, silencing of SCaM4 did not alter susceptibility to any of these three pathogens. Furthermore, the SCaM4-overexpressing soybean plants exhibited increased tolerance to high salt conditions. To understand the mechanisms involved in SCaM4-mediated pathogen resistance, we evaluated expression levels of pathogenesis-related (PR) genes. Our studies revealed a significant increase in levels of expression of the PR genes, deemed as indicators of systemic acquired resistance (SAR). Interaction of SCaM4 and the nucleus-localized SAR-regulatory GmNPR1 proteins is proposed as the mechanism-underlying enhancement of PR gene expression and resistance to pathogens. To investigate SCaM4-mediated high-salt tolerance, we confirmed the interaction between SCaM4 and the stress responsive gene regulating transcription factor protein Myb2 using the yeast two-hybrid system. We also studied the subcellular localization pattern of SCaM4 using a GFP-SCaM4 fusion construct. Confocal microscopic observation has suggested that SCaM4 is localized in the nucleus, cytoplasm, and chloroplasts.