English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Turnips (Brassica rapa. subsp. rapa L.) produce glucosinolates (GSLs), thioglucosides whose hydrolyzed derivatives have been shown to provide chemopreventive benefits. Two cultivars of turnips [‘Just Right’ (JR) and ‘Scarlet Queen’ (SQ)] were grown under three different temperature regimes to assess the role of temperature on GSL production in roots and shoots. When compared with low-temperature treatments, high-temperature treatments increased total and individual GSLs in a tissueand genotype-specific manner. When compared with low-temperature treatments, total GSLs were ’70% and 130% higher in JR shoots and roots, respectively, grown at high-temperature treatments. High temperatures also increased total GSLs in SQ shoots and roots by ’80% and 85%, respectively, when compared with low temperatures. Gluconasturtiin (GNS, 2-phenylethyl GSL) concentration was inversely correlated with temperature with high-temperature treatments resulting in 20% and 48% less GNS than low-temperature treatments in JR and SQ roots, respectively. The indolic GSL, 1-methoxyglucobrassicin (1MGB; 1-methoxy-3-ylmethyl GSL), was the root GSL most elevated by increased temperature resulting in a 1000% increase on average in both cultivars between the lowand high-temperature treatments. These results show promise for the use of temperature to enhance the health-promoting properties of turnip because 1MGB has potent chemopreventive effects. Gene expression analysis suggests that some BrMYB transcription factor expression levels are associated with temperaturedependent changes in GSL accumulation; however, this association varies between cultivar and tissue type. Glucosinolates are thioglucosides found in Brassica vegetables that when hydrolyzed at the S-glucose bond create a suite of products involved in plant defense, flavor, and human health. Consumption of vegetables containing glucosinolates has been correlated with cancer and disease prevention (Hecht, 2000; Talalay and Fahey, 2001) Glucosinolates and their hydrolyzed derivatives, mainly isothiocyanates, have been shown to serve as chemopreventive agents by stimulating both protection from and excretion of carcinogens and by inhibiting tumor growth (Hecht, 2000; Neave et al., 2005). Identifying vegetable production systems that enhance GSL concentrations could have a significant impact on human health, particularly cancer prevention. GSL concentration is highly influenced by genotype and environmental factors including soil fertility, temperature, and light (Antonious et al., 1996; Charron and Sams, 2004; Engelen-Eigles et al., 2006; Rosen et al., 2005). We found strong correlations between GSL concentrations and temperature in field experiments using colored plastic mulches (Justen et al., 2011). Our previous research using colored plastic mulches in a field setting demonstrated that plastic mulches both alter the light reflected into the canopy of turnip plants and also appreciably change soil temperature (Justen et al., 2011). Depending on the planting date and type of mulch, average soil temperatures under mulches during the turnip growing season can be up to 5 C above and 4 C below bare soil temperatures (Justen et al., 2011). Temperature can have a significant impact on both shoot and root GSL concentration in a controlled environment. Charron and colleagues found that the concentration of the aliphatic glucosinolate gluconapin (GNP; 3-butenyl GSL) doubled in leaves and stems of B. oleracea plants grown at 32 C and the indolic glucosinolate 1MGB (neoglucobrassicin; 1-methoxy-3-ylmethyl GSL) increased 3-fold in roots grown at 32 C compared with those grown at 12 C (Charron and Sams, 2004). Engelen-Eigles and colleagues (2006) found that the concentration of the aromatic glucosinolate gluconasturtiin was increased in Nasturtium officinale grown at 10 and 15 C as compared with that grown at 20 or 25 C. Both aliphatic and indolic GSL biosynthesis are regulated by various genetic components. In Arabidopsis, such regulatory elements can repress GSL production such as SLIM1 (Sulfur Limitation1; MaruyamaNakashita et al., 2006), promote GSL production such as AtDof1.1 (DNA-binding-with-one finger; Skirycz et al., 2006) and subgroup 12 R2-R3 MYB transcription factors (Gigolashvili et al., 2009), or both positively and negatively regulate GSL production such as the nuclear-localized calmodulin-binding protein IQD1 (Levy et al., 2005). Two distinct clades of subgroup 12 R2-R3 MYB transcription factors regulate GSL biosynthesis and accumulation. Clade 1 members MYB34, MYB51, and MYB122 regulate indolic GSL biosynthesis, whereas clade 2 members MYB28, MYB29, and MYB76 regulate aliphatic GSL biosynthesis (Gigolashvili et al., 2009). Members within each clade appear to have distinct but overlapping roles. It has been suggested that MYB34, MYB122, and MYB 51 positively regulate glucobrassicin, but only MYB51 positively regulates other GSLs such as methoxylated indolic glucosinolates (Gigolashvili et al., 2007). However, Malitsky and colleagues (2008) did not observe this trend and found that both MYB34 and MYB51 overexpression resulted in increases in 1-methoxyglucobrassicin. MYB28 regulates both long(6 to 8 carbon length) and short-chain (3 to 5 carbon length) aliphatic GSL biosynthesis and its overexpression can result in increased accumulation of indolic GSLs (Hirai et al., 2007). MYB29 and MYB76 also regulate GSL biosynthesis to a lesser degree, but only short-chain aliphatic GSL biosynthesis (Gigolashvili et al., 2008; Sønderby et al., 2007). MYB transcription factors may also regulate GSL biosynthesis in a tissue-specific manner with MYB34 and MYB122 being preferentially expressed in root tissues and MYB51 being preferentially expressed in leaf tissue (Gigolashvili et al., 2009). MYB28, MYB29, and MYB76 appear to be expressed to some degree in all tissues (Gigolashvili et al., 2009). In most cases, the expression pattern of MYB transcription factors correlates with expression of other GSL biosynthetic genes (Gigolashvili et al., 2009). No MYB transcription factors have been identified that specifically regulate aromatic GSL biosynthesis. Using a comparative genomics approach, Zang and colleagues (2009) identified GSL biosynthetic and regulatory orthologs in Received for publication 30 Aug. 2012. Accepted for publication 15 Nov. 2012. We thank Dr. Adrian Hegeman for the use of his UPLC-MS and Doug Brinkman for technical support. To whom reprint requests should be addressed; e-mail vafritz@umn.edu. HORTSCIENCE VOL. 48(1) JANUARY 2013 47 Brassica rapa (Br) with high sequence identity (72% to 94%) to Arabidopsis thaliana GSL biosynthetic genes. In most cases, multiple copies of these genes were found in B. rapa (Zang et al., 2009). Two MYB transcription factor orthologs, MYB76 and MYB122, were absent or non-functional in B. rapa. BrMYB122-1 was found to be nonfunctional as a result of a deletion that resulted in a premature stop codon, whereas MYB76 was absent in B. rapa (Zang et al., 2009). The absence of MYB76 in B. rapa is interesting because MYB76 positively regulates methylsulfinylated short-chained aliphatic GLSs in Arabidopsis (Sønderby et al., 2010) and these GLSs are absent or in low concentrations in turnip (Carlson et al., 1987; Li et al., 2007; Smetanska et al., 2007). Although GSL-associated MYB orthologs from Arabipdopsis have been identified in B. rapa through comparative genomics (Zang et al., 2009), there is little data on the influence of these MYBs on GSL accumulation in B. rapa. It is possible that tissue-dependent changes in BrMYB transcription may result in tissue-dependent changes in GSL accumulation observed in turnips grown at different temperatures. Genotype can be a major factor in determining baseline GSL concentration in plant tissues. Rosen and colleagues (2005) found that red cabbage had inherently higher GSL content than green cabbage. We previously found that roots of the red-skinned turnip cultivar Scarlet Queen have inherently higher GSL levels than purple-crown and whiteskinned turnip roots (Justen et al., 2011) Genotypes can also vary in terms of GSL enhancement by environmental factors (Fritz et al., 2010; Justen et al., 2011; Rosen et al., 2005). The objective of this experiment was to quantify shoot and root tissue GSL concentrations of two turnip cultivars, Just Right and Scarlet Queen, under three different temperature regimes representing the range of soil temperatures present in our previous plastic mulch experiment. We also sought to examine the relationship between temperature and GSL biosynthesis regulation by quantifying transcript levels of BrMYB orthologs in turnips grown at different temperatures. These MYB orthologs have been shown to regulate GSL biosynthesis in Arabidopsis. Materials and Methods Growth chamber conditions and plant materials. Turnip seeds (cv. Just Right; Jordan’s Seed, Woodbury, MN, and cv. Scarlet Queen; Johnny’s Seeds, Winslow, ME) were grown in a soilless media (Sunshine Grow Mix LC-8; Sun Gro Horticulture, Bellevue, WA) in 10-cm pots. The plants were grown for 42 d under three different air temperature treatments (Table 1) with a relative humidity of 75%. The photoperiod was 14 h with a constant photosynthetically active radiation (PAR) of 475 mmol·m·s and a red:far-red ratio of 2.1. Plants were grown in a model GCW-15 growth chamber (Environmental Growth Chambers, Chagrin Falls, OH) fitted with metal halide bulbs. Plantlets were thinned to one plant per pot 1 week after seedling emergence. Plants were watered daily and fertilized weekly with 200 ppm nitrogen using 20–10–20 Peat-lite Water Soluble Fertilizer (Scotts Miracle-Gro Company, Marysville, OH). All sampling was carried out between 0900 and 1100 HR. The experiment was replicated twice over time. JR and SQ plants were arranged in a completely randomized design of four replications within each growth chamber. Turnip plants were harvested 6 weeks after seeding and

Temperature-induced Glucosinolate Accumulation Is Associated with Expression of BrMYB Transcription Factors