Abstract
Phytopathogens and pests are two major factors that limit the growth of plants. The expression of a flavonoid regulator gene, AtMYB12(AT2G47460), has been reported to increase the endogenous flavonoid content of tobacco and tomato. Previous research has only focused on the regulation mechanism of v-myb avian myeloblastosis viral oncogene homolog (MYB) transcription factors under single stress conditions. Here, research showed that AtMYB12 was involved in regulating the resistance of tobacco to multiple biological stresses such as phytopathogens and aphid. We reported that transgenic tobacco carrying AtMYB12 was more resistant to Ralstonia solanacearum when the up-regulated expression of several defense-related markers, such as NbPR1a, NbNOA1, and NbrbohB, was activated, suggesting that the priming defense of a plant may contribute to bacterial disease resistance. The improvement of the resistance of AtMYB12-expressing transgenic tobacco is achieved by promoting the production of ROS, H2O2, and NO. AtMYB12-expressing transgenic tobacco also has resistance to fungal pathogens, such as Colletotrichum nicotianae Averna and Alternaria alternate. The enrichment of flavonols components, such as rutin, which directly inhibit the growth of C. nicotianae and A. alternate, may also contribute to the defense mediated by AtMYB12 over-expression. At the same time, the results also confirm that AtMYB12-expressing transgenic tobacco enhanced plant resistance to aphid-infested (Aphidoidea) pests. These results suggest that the AtMYB12 gene is a good candidate for pest and disease control, with limited resistance costs and enrichment in flavonols, and that AtMYB12 has a potential in the breeding of disease-resistant tobacco crops.
Highlights
Flavonoids are a large class of secondary metabolites that are widely present in the plant kingdom and encompass over 9,000 molecules (Cheynier et al, 2013)
In AtMYB12-expressing transgenic tobacco, rutin was the predominant flavonol in the methanolic extract
The increased level of flavonol in tobacco was substantially higher than those demonstrated for AtMYB12 overexpression in Arabidopsis, which showed a three- to four-fold increase in the transgenic plants (Mehrtens et al, 2005), but less than the original report of a 46-fold increase for rutin in tobacco (Luo et al, 2008)
Summary
Flavonoids are a large class of secondary metabolites that are widely present in the plant kingdom and encompass over 9,000 molecules (Cheynier et al, 2013). Flavonoids are reported to play a significant role in plant resistance, both in terms of abiotic and biotic stresses (Nayak et al, 2015), such as drought, UV radiation, and heavy metal contamination (Izaguirre et al, 2007; Lei et al, 2019). In addition to their function in abiotic stress resistance, flavonoids have been found to be involved in plant protection. Some flavonoids, such as naringenin, kaempferol, quercetin, and dihydroquercetin, show an inhibition effect on the gingipain activity of Porphyromonas gingivalis (Kariu et al, 2017)
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