P-087 - LOB1: A Master Susceptibility Gene Regulating Citrus Transcriptome Reprogramming in Response to Canker Pathogen

Citrus canker is one of the most significant diseases affecting citrus. It is caused by the bacterial pathogen Xanthomonas citri pv. citri (Xcc). We previously demonstrated that editing the LOB1 TAL effector binding element (EBE) region using CRISPR/Cas9 conferred resistance to Xcc in mutant plants (Huang et al., Front. Plant Sci. 12:769907 (2022)). Using the base editor ABE8e, we further showed that the TATA box upstream of the LOB1 EBE is essential for LOB1 induction by the TAL effector PthA4 (Huang et al., Front. Genome Ed. 4:852867 (2022)). When this TATA box was edited into CACA, mutant plants became resistant to Xcc. To develop market-friendly, canker-resistant citrus germplasm, we invented a co-editing strategy to generate transgene-free, canker-resistant citrus plants in T0 by editing the LOB1 EBE region (Huang et al., Nat. Plants 9, 1591–1597 (2023)). Since the LOB1 protein functions as a transcription regulator, we knocked out the LOB1 coding region to explore its function using CRISPR/Cas9 system (Huang et al., Plant Mol. Biol. 104, 297–307 (2020)). Both WT and mutant plants, with or without Xcc inoculation, were subjected to RNA-seq analysis. Interestingly, most of the LOB1-induced genes (403 genes in WT, using a two-fold induction as the cutoff) were no longer induced in lob1 mutant plants (only 13 genes induced) 24 hpi. RT-qPCR confirmed that some genes, such as expansin, gibberellin-regulated 4, and RbohD, were upregulated in WT plants but not in lob1 mutants. We are growing these LOB1-edited plants along WT and are observing agronomic traits.