Identification of flavonoids as regulators of YbeY activity in Liberibacter asiaticus

Abstract

Summary Liberibacter asiaticus is the prevalent causative pathogen of Huanglongbing or citrus greening disease, which has resulted in a devastating crisis in the citrus industry. A thorough understanding of this pathogen's physiology and mechanisms to control cell survival is critical in the identification of therapeutic targets. YbeY is a highly conserved bacterial RNase that has been implicated in multiple roles. In this study, we evaluated the biochemical characteristics of the L. asiaticus YbeY (CLIBASIA_01560) and assessed its potential as a target for antimicrobials. YbeYLas was characterized as an endoribonuclease with activity on 3′ and 5′ termini of 16S and 23S rRNAs, and the capacity to suppress the E. coli ΔybeY phenotype. We predicted the YbeYLas protein:ligand interface and subsequently identified a flavone compound, luteolin, as a selective inhibitor. Site‐directed mutagenesis was subsequently used to identify key residues involved in the catalytic activity of YbeYLas. Further evaluation of naturally occurring flavonoids in citrus trees indicated that both flavones and flavonols had potent inhibitory effects on YbeYLas. Luteolin was subsequently examined for efficacy against L. asiaticus in Huanglongbing‐infected citrus trees, where a significant reduction in L. asiaticus gene expression was observed.

YBEY is an essential biogenesis factor for mitochondrial ribosomes

“…Moreover, substitution H128A, which lowers the RNase activity of the recombinant human enzyme, does not affect its ability to complement a YBEY KO, similar to the equivalent substitution in E. coli ( 8 ). Likewise, substitution R55A, which severely impairs the RNase activity of bacterial YbeY ( 5 , 12 ), fully complements YBEY deletion in humans and B. subtilis ( 3 ) and restores 16S rRNA processing in E. coli ( 8 ), B. subtilis ( 3 ) and Liberibacter asiaticus ( 19 ). These observations suggest that the apparent RNase activity of YBEY is not necessarily related to ribosome biogenesis, calling for further studies to clarify its nature and significance.…”

“…Mechanistically, YbeY has been described as a metal-dependent endoribonuclease ( 5 , 12 , 18 ), and in some bacteria, ybeY mutants accumulate 16S rRNA with an unprocessed 3′ end ( 3 , 5 , 7 , 8 , 18 , 19 ). Therefore, YbeY was proposed to be the ‘missing’ 3′ endoribonuclease required for 16S rRNA maturation to obtain the correct anti-Shine-Dalgarno sequence, which is needed for translation initiation on most bacterial mRNAs.…”

Phenolics, flavonoids and antioxidant capacities inCitrusspecies with different degree of tolerance to Huanglongbing

“…In addition, the YbeY portion of the bacterium's genetic code was found to play an important role in bacterial symbiosis and pathogenicity. 38 Tested flavones and flavonols showed a significant reduction in CLas titer in HLBinfected citrus trees. 38 On the other hand, the flavanones (hesperetin and naringenin) were found to have little to no inhibitory effect.…”

“…9 Flavonoids, which are also considered as a group of phenolic compounds, have a good antioxidant activity. 26,37 Recently, Zuo et al (2019) showed that flavones such as luteolin and apigenin and flavonols (quercetin) had potent inhibitory effects on YbeY of CLas bacterium. 38 YbeY is considered part of the 206 genes that make up the minimal bacterial genome set, which is necessary for the maturation of RNAs.…”

“…26,37 Recently, Zuo et al (2019) showed that flavones such as luteolin and apigenin and flavonols (quercetin) had potent inhibitory effects on YbeY of CLas bacterium. 38 YbeY is considered part of the 206 genes that make up the minimal bacterial genome set, which is necessary for the maturation of RNAs. In addition, the YbeY portion of the bacterium's genetic code was found to play an important role in bacterial symbiosis and pathogenicity.…”