Abstract
BackgroundOzone is an air pollutant widely known to cause a decrease in productivity in many plant species, including soybean (Glycine max (L.) Merr). While the response of cultivated soybean to ozone has been studied, very little information is available regarding the ozone response of its wild relatives.ResultsOzone-resistant wild soybean accessions were identified by measuring the response of a genetically diverse group of 66 wild soybean (Glycine soja Zucc. and Sieb.) accessions to elevated ozone levels. RNA-Seq analyses were performed on leaves of different ages from selected ozone-sensitive and ozone-resistant accessions that were subjected to treatment with an environmentally relevant level of ozone. Many more genes responded to elevated ozone in the two ozone-sensitive accessions than in the ozone-resistant accessions. Analyses of the ozone response genes indicated that leaves of different ages responded differently to ozone. Older leaves displayed a consistent reduction in expression of genes involved in photosynthesis in response to ozone, while changes in expression of defense genes dominated younger leaf tissue in response to ozone. As expected, there is a substantial difference between the response of ozone-sensitive and ozone-resistant accessions. Genes associated with photosystem 2 were substantially reduced in expression in response to ozone in the ozone-resistant accessions. A decrease in peptidase inhibitors was one of several responses specific to one of the ozone resistant accessions.ConclusionThe decrease in expression in genes associated with photosynthesis confirms that the photosynthetic apparatus may be an early casualty in response to moderate levels of ozone. A compromise of photosynthesis would substantially impact plant growth and seed production. However, the resistant accessions may preserve their photosynthetic apparatus in response to the ozone levels used in this study. Older leaf tissue of the ozone-resistant accessions showed a unique down-regulation of genes associated with endopeptidase inhibitor activity. This study demonstrates the existence of significant diversity in wild soybean for ozone response. Wild soybean accessions characterized in this study can be used by soybean breeders to enhance ozone tolerance of this important food crop.
Highlights
Ozone is an air pollutant widely known to cause a decrease in productivity in many plant species, including soybean (Glycine max (L.) Merr)
Ozone reacts with many different molecules in the apoplast of leaves to produce different harmful products known as Reactive Oxygen Species (ROS), such as OH− radicals and hydrogen peroxide [9, 10]
Analysis of RNA transcripts from selected ozone sensitive and resistant wild soybean lines Ninety-five samples were collected from four biological replicates of the first three fully expanded trifoliates (T1T3) from both O3-treated (75 ppb) and charcoal-filtered (CF) air treated plants of Plant introduction (PI) 424007 (S), PI 407179 (S), PI 424123 (R) and PI 507656 (R)
Summary
Ozone is an air pollutant widely known to cause a decrease in productivity in many plant species, including soybean (Glycine max (L.) Merr). The deleterious effects of ozone (O3) on agriculture have been of increasing concern. As populations rise and technology advances, it is expected that these levels could increase to 75 ppb by the year 2050 [3]. Ozone reacts with many different molecules in the apoplast of leaves to produce different harmful products known as Reactive Oxygen Species (ROS), such as OH− radicals and hydrogen peroxide [9, 10]. The capacity of the apoplast to detoxify ROS is a primary defense mechanism of the plant to ozone stress [11]. After exposure to O3 levels of >40 ppb, stress responses
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