Abstract
SummarySoybean (Glycine max (L.) Merr.) salicylic acid methyl transferase (GmSAMT1) catalyses the conversion of salicylic acid to methyl salicylate. Prior results showed that when GmSAMT1 was overexpressed in transgenic soybean hairy roots, resistance is conferred against soybean cyst nematode (SCN), Heterodera glycines Ichinohe. In this study, we produced transgenic soybean overexpressing GmSAMT1 and characterized their response to various SCN races. Transgenic plants conferred a significant reduction in the development of SCN HG type 1.2.5.7 (race 2), HG type 0 (race 3) and HG type 2.5.7 (race 5). Among transgenic lines, GmSAMT1 expression in roots was positively associated with SCN resistance. In some transgenic lines, there was a significant decrease in salicylic acid titer relative to control plants. No significant seed yield differences were observed between transgenics and control soybean plants grown in one greenhouse with 22 °C day/night temperature, whereas transgenic soybean had higher yield than controls grown a warmer greenhouse (27 °C day/23 °C night) temperature. In a 1‐year field experiment in Knoxville, TN, there was no significant difference in seed yield between the transgenic and nontransgenic soybean under conditions with negligible SCN infection. We hypothesize that GmSAMT1 expression affects salicylic acid biosynthesis, which, in turn, attenuates SCN development, without negative consequences to soybean yield or other morphological traits. Thus, we conclude that GmSAMT1 overexpression confers broad resistance to multiple SCN races, which would be potentially applicable to commercial production.
Highlights
In the United States, the soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is the most damaging pest to soybean (Glycine max [L.] Merr.) (Koenning and Wrather, 2010)
We previously identified a soybean salicylic acid methyl transferase gene (GmSAMT1) as a candidate SCN defencerelated gene (Mazarei et al, 2011) and studied SCN race 2 (HG type 1.2.5.7) development in soybean hairy roots overexpressing GmSAMT1 (Lin et al, 2013)
PCR analysis showed that GmSAMT1 and Bar genes were stably inherited in these soybean lines (Figure S1)
Summary
In the United States, the soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is the most damaging pest to soybean (Glycine max [L.] Merr.) (Koenning and Wrather, 2010). Most SCN-resistance QTL can be traced to ‘Peking’ PI 437654 and PI 88788 (Concibido et al, 2004), which provide some resistance to SCN races 2, 3 and 5 (Guo et al, 2005). Genes cloned from two QTL from PI 88788 and cultivar ‘Forrest’ (Cook et al, 2012; Liu et al, 2012) have provided new insights into understanding of SCN resistance mechanisms. The most well-known resistance QTL are located on chromosomes 18 (rhg1) and 8 (Rhg4), which are considered to be the major sources of resistance in soybean cultivars (Concibido et al, 2004).
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