Poster: Molecular & Cellular Plant-Microbe Interactions: MPMI
Expression of FLS2s from ‘Nagami’ kumquat and ‘Sun Chu Sha’ mandarin enhance citrus canker resistance in ‘Duncan’ grapefruit
V. FEBRES (1), Q. Shi (1), G. Moore (1) (1) University of Florida, U.S.A.
In citrus, flagellin 22 (flg22), a pathogen-associated molecular pattern (PAMP) from Xanthomonas citri ssp. citri (Xflg22), triggers stronger defense responses in canker resistant genotypes than susceptible ones (Shi et al. Mol. Plant Pathol. 2025, 16:507). We have now identified the citrus genes encoding putative bacterial flagellin/flg22 receptors (FLS2). We isolated two genes each from ‘Sun Chu Sha’ mandarin (Citrus reticulata, CrFLS2-1 and CrFLS2-2) and ‘Duncan’ grapefruit (C. paradisi, CpFLS2-1 and CpFLS2-2), a canker resistant and a highly susceptible citrus species, respectively. Only one FLS2 gene was obtained from the highly canker-resistant ‘Nagami’ kumquat (Fortunella margarita, FmFLS2-1). Flanking sequences suggest a rearrangement event resulted in the deletion of FLS2-2 from the genome of kumquat. Transcriptional analysis indicated that the FLS2-2s reached higher expression levels in response to Xflg22 than the FLS2-1s, and the induction levels positively correlated with the level of canker resistance. Kumquat showed the highest FLS2-1 pre-treatment expression level among the citrus species tested. We also transiently expressed FmFLS2-1, CrFLS2-2 and CpFLS2-2 in leaves of susceptible grapefruit. FmFLS2-1 and CrFLS2-2 conferred stronger responses to Xflg22 and reduced canker symptom development when compared to CpFLS2-2. We conclude that these two genes are valuable for engineering enhanced canker resistance and possibly other bacterial pathogens.