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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPACT OF CLIMATE CHANGE ON PLANT DEFENSE RESPONSES INDUCED BY INSECT HERBIVORES AND PLANT PATHOGENS

Location: Chemistry Research Unit

Title: Drought stress suppresses phytoalexin production against Fusarium verticilliodes

Authors
item Vaughan, Martha
item Huffaker, Alisa
item Schmelz, Eric
item Callis, Kristine -
item Dafoe, Nicole
item Allen, Leon
item Teal, Peter

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 7, 2011
Publication Date: N/A

Interpretive Summary: Global climate change involves rising temperatures and potentially decreased rainfall or changes in rainfall patterns, which could dramatically decrease the yield of food crops. Drought alone can impair plant growth and development, but in nature plants are continuously exposed to both abiotic and biotic stresses. Fusarium verticillioides is an important fungal pathogen of Zea mays that causes seedling decay, stalk rot, ear rot, and produces carcinogenic mycotoxins, namely fumonisins. Consumption of fumonisins from contaminated food can cause serious illness that affect both humans and animals. Effects range from weight loss and reproductive abnormalities, to organ failure, cancer and death. Water stress, elevated temperatures and herbivore damage are ideal environmental conditions that promote F. verticilliodes growth and fumonisin production. Relatively little is known about the effects of climate change on Zea mays defense strategies against F. verticilliodes. In this study, we inoculated the stem of Zea mays var. Golden Queen with F. verticilliodes and measured the production of phytoalexins under normal (watered) and drought stress conditions. At the site of F. verticilliodes inoculation a significant decrease in terpenoid phytoalexin production was detected in drought stressed plants as compared to those under normal conditions. Phytoalexin production is stimulated through the jasmomic acid (JA)- ethylene signaling pathway. JA production was suppressed in drought stressed plants infected with F. verticilliodes. One possible explanation for this suppression would be an increase in abscisic acid (ABA), a photohormone produced in response to water-deficit conditions. ABA is thought to inhibit JA- ethylene dependent resistance. Although, we did not detect a significant increase of ABA in drought stressed plants inoculated with F. verticilliodes, ABA may have been elevated an earlier time point or before the addition of the fungal pathogen. The existence of an ABA-independent signal transduction cascade between the initial stress signal and the expression of drought- specific genes has previously been suggested and may also suppress JA-ethylene responses. Unlike the infected stem tissue, the control drought stressed roots had increased phytoalexin concentrations. This did not coincide with significantly elevated JA, however, the JA induction may have preceded the 48 hr time point. Plants tolerate stress by activating signal transduction cascades that interact with each other in order to control and coordinate the physiological and biochemical responses necessary for adaptation and survival. Through these interacting signaling cascades plants may redirect defense metabolites to the tissue of most importance, which in the case of a drought stressed plant would be the roots. Our results suggest that the perception and response to abiotic stress may dictate or alter subsequent biotic stress responses.

Technical Abstract: Global climate change involves rising temperatures and potentially decreased rainfall or changes in rainfall patterns, which could dramatically decrease the yield of food crops. Drought alone can impair plant growth and development, but in nature plants are continuously exposed to both abiotic and biotic stresses. Fusarium verticillioides is an important fungal pathogen of Zea mays that causes seedling decay, stalk rot, ear rot, and produces carcinogenic mycotoxins, namely fumonisins. Consumption of fumonisins from contaminated food can cause serious illness that affect both humans and animals. Effects range from weight loss and reproductive abnormalities, to organ failure, cancer and death. Water stress, elevated temperatures and herbivore damage are ideal environmental conditions that promote F. verticilliodes growth and fumonisin production. Relatively little is known about the effects of climate change on Zea mays defense strategies against F. verticilliodes. In this study, we inoculated the stem of Zea mays var. Golden Queen with F. verticilliodes and measured the production of phytoalexins under normal (watered) and drought stress conditions. At the site of F. verticilliodes inoculation a significant decrease in terpenoid phytoalexin production was detected in drought stressed plants as compared to those under normal conditions. Phytoalexin production is stimulated through the jasmomic acid (JA)- ethylene signaling pathway. JA production was suppressed in drought stressed plants infected with F. verticilliodes. One possible explanation for this suppression would be an increase in abscisic acid (ABA), a photohormone produced in response to water-deficit conditions. ABA is thought to inhibit JA- ethylene dependent resistance. Although, we did not detect a significant increase of ABA in drought stressed plants inoculated with F. verticilliodes, ABA may have been elevated an earlier time point or before the addition of the fungal pathogen. The existence of an ABA-independent signal transduction cascade between the initial stress signal and the expression of drought- specific genes has previously been suggested and may also suppress JA-ethylene responses. Unlike the infected stem tissue, the control drought stressed roots had increased phytoalexin concentrations. This did not coincide with significantly elevated JA, however, the JA induction may have preceded the 48 hr time point. Plants tolerate stress by activating signal transduction cascades that interact with each other in order to control and coordinate the physiological and biochemical responses necessary for adaptation and survival. Through these interacting signaling cascades plants may redirect defense metabolites to the tissue of most importance, which in the case of a drought stressed plant would be the roots. Our results suggest that the perception and response to abiotic stress may dictate or alter subsequent biotic stress responses.

Last Modified: 8/21/2014