Flavonone 3-hydroxylase Relieves Bacterial Leaf Blight Stress in Rice via Overaccumulation of Antioxidant Flavonoids and Induction of Defense Genes and Hormones

Abstract

Efficient accumulation of flavonoids is important for increased tolerance to biotic stress. Although several plant defense mechanisms are known, the roles of many pathways, proteins, and secondary metabolites in stress tolerance are unknown. We generated a flavanone 3-hydroxylase (F3H) overexpressor rice line and inoculated Xanthomonas Oryzae pv. oryzae and compared the control and wildtype inoculated plants. In addition to promoting plant growth and developmental maintenance, the overexpression of F3H increased the accumulation of flavonoids and increased tolerance to bacterial leaf blight (BLB) stress. Moreover, leaf lesion length was higher in the infected wildtype plants compared with infected transgenics. Kaempferol and quercetin, which scavenge reactive oxygen species, overaccumulated in transgenic lines compared with wildtypes in response to pathogenic infection, detected by scanning electron microscopy and spectrophotometry. The induction of F3H altered the antioxidant system and reduced the levels of glutathione peroxidase activity and malondialdehyde (MDA) contents in the transgenic lines compared with the wildtypes. Downstream gene regulation analysis showed that the expression of F3H increased the regulation of flavonol synthase (FLS), dihydroflavonol 4-reductase (DFR), and slender rice mutant (SLR1) during BLB stress. The analysis of SA and JA signaling revealed an antagonistic interaction between both hormones and that F3H induction significantly promoted SA and inhibited JA accumulation in the transgenic lines. SA-dependent nonexpressor pathogenesis-related (NPR1) and Xa1 showed significant upregulation in the infected transgenic lines compared with the infected control and wildtype lines. Thus, the overexpression of F3H was essential for increasing BLB stress tolerance.

Deciphering of Pod Borer [Helicoverpa armigera (Hübner)] Resistance in Cajanus platycarpus (Benth.) Offers Novel Insights on the Reprogramming and Role of Flavonoid Biosynthesis Pathway

“…Fascinatingly, pivotal branch point enzymes in the flavonoid biosynthesis pathway, initially CHS, a pertinent player in the production of flavonones such as naringenin and later flavonols such as quercetin and kaempferol was seen to be upregulated coordinating with the over-accumulation of the metabolites. The wild relative also depicted reallocation of resources for the overexpression of specific isoforms of F3′H, FLS, F3′5′H, and DFR that compete with dihydrokaempferol for the initiation of the production of anthocyanins ( Figure 3 ) [ 47 , 48 , 49 ]. Fine orchestration of molecular events was seen in the pigeonpea wild relative with strategic channeling of resources for the significant ( p < 0.05) accumulation of epicatechin-3-gallate and epigallocatechin to the maximum extent through the induced expression of LDOX and F3′5′H ( Figure 3 ).…”

Integrated transcriptomic and transgenic analyses reveal potential mechanisms of poplar resistance to Alternaria alternata infection

“…For example, the expression of CHS in soybean is upregulated during both fungal and bacterial pathogen infection [42]. The overexpression of OxF3H in rice increased tolerance to bacterial leaf blight [43]. In this study, DEGs related to avonoid biosynthesis, including CHS, F3H, DFR and LDOX, were induced by A. alternata infection, especially at the early stage of infection (Fig.…”

Integrated transcriptomic and transgenic analyses reveal potential mechanisms of poplar resistance to Alternaria alternata infection

“…For example, the expression of CHS in soybean is upregulated during both fungal and bacterial pathogen infection [ 42 ]. Overexpression of OxF3H in rice increased tolerance to bacterial leaf blight [ 43 ]. In this study, DEGs related to flavonoid biosynthesis, including CHS , F3H , DFR and LDOX, were induced by A. alternata infection, especially at the early stage of infection (Fig.…”