Lipoxygenases regulate digestive enzyme inhibitor activities in developing seeds of field-grown soybean against the southern green stink bug (Nezara viridula).

Soybean (Glycine max ) is the world's most widely grown seed legume. One of the most important pests that decrease seed quality and reduce yield of soybean crops is the southern green stink bug (Nezara viridula ). Insect damage triggers accumulation of defensive compounds such as protease inhibitors (PIs), isoflavonoids and reactive oxygen species, which are regulated by the lipoxygenase (LOX)-regulated jasmonic acid (JA) to stop insect feeding. This study identified and characterised the role of LOX isoforms in the modulation of chemical defences in seeds of field-grown soybean that decreased digestive enzyme activities of N. viridula after insect attack. Stink bugs attack increased LOX 1 and LOX 2 expression, and activities of LOX 1 and LOX 3 isoenzymes in developing soybean seeds. In addition, stink bug damage and methyl jasmonate application induced expression and activity of both cysteine PIs and trypsin PIs in developing soybean seeds, suggesting that herbivory induced JA in soybean seeds. High PI activity levels in attacked seeds decreased cysteine proteases and α-amylases activities in the gut of stink bugs that fed on field-grown soybean. We demonstrated that LOX isoforms of seeds are concomitantly induced with JA-regulated PIs by stink bugs attack, and these PIs inhibit the activity of insect digestive enzymes. To our knowledge, this is the first study to investigate the participation of LOX in modulating JA-regulated defences against stink bugs in seeds of field-grown soybean, and our results suggest that soybean PIs may inhibit α-amylase activity in the gut of N. viridula .

Characterized non-transient microbiota from stinkbug (Nezara viridula) midgut deactivates soybean chemical defenses.

The Southern green stinkbug (N. viridula) feeds on developing soybean seeds in spite of their strong defenses against herbivory, making this pest one of the most harmful to soybean crops. To test the hypothesis that midgut bacterial community allows stinkbugs to tolerate chemical defenses of soybean developing seeds, we identified and characterized midgut microbiota of stinkbugs collected from soybean crops, different secondary plant hosts or insects at diapause on Eucalyptus trees. Our study demonstrated that while more than 54% of N. viridula adults collected in the field had no detectable bacteria in the V1-V3 midgut ventricles, the guts of the rest of stinkbugs were colonized by non-transient microbiota (NTM) and transient microbiota not present in stinkbugs at diapause. While transient microbiota Bacillus sp., Micrococcus sp., Streptomyces sp., Staphylococcus sp. and others had low abundance, NTM microbiota was represented by Yokenella sp., Pantoea sp. and Enterococcus sp. isolates. We found some isolates that showed in vitro ß-glucosidase and raffinase activities plus the ability to degrade isoflavonoids and deactivate soybean protease inhibitors. Our results suggest that the stinkbugs´ NTM microbiota may impact on nutrition, detoxification and deactivation of chemical defenses, and Enterococcus sp., Yokenella sp. and Pantoea sp. strains might help stinkbugs to feed on soybean developing seeds in spite of its chemical defenses.

Early perception of stink bug damage in developing seeds of field-grown soybean induces chemical defences and reduces bug attack.

BACKGROUND: Southern green stink bugs (Nezara viridula L.) invade field-grown soybean crops, where they feed on developing seeds and inject phytotoxic saliva, which causes yield reduction. Although leaf responses to herbivory are well studied, no information is available about the regulation of defences in seeds. RESULTS: This study demonstrated that mitogen-activated protein kinases MPK3, MPK4 and MPK6 are expressed and activated in developing seeds of field-grown soybean and regulate a defensive response after stink bug damage. Although 10-20 min after stink bug feeding on seeds induced the expression of MPK3, MPK6 and MPK4, only MPK6 was phosphorylated after damage. Herbivory induced an early peak of jasmonic acid (JA) accumulation and ethylene (ET) emission after 3 h in developing seeds, whereas salicylic acid (SA) was also induced early, and at increasing levels up to 72 h after damage. Damaged seeds upregulated defensive genes typically modulated by JA/ET or SA, which in turn reduced the activity of digestive enzymes in the gut of stink bugs. Induced seeds were less preferred by stink bugs. CONCLUSION: This study shows that stink bug damage induces seed defences, which is perceived early by MPKs that may activate defence metabolic pathways in developing seeds of field-grown soybean. © 2015 Society of Chemical Industry.