P-046 - Genetic architecture of Sieve Element Occlusion (SEO) family reveals potential genetic regulations associated with Citrus Huanglongbing (HLB)

SEO proteins mediate reversible sieve plate occlusion, a key defense mechanism in Citrus against HLB. Their genes are highly induced in susceptible but downregulated in tolerant species upon Candidatus Liberibacter asiaticus colonization. Despite their importance, the SEO gene family remains poorly characterized. Here, we analyzed 27 SEO genes in Citrus species with contrasting HLB tolerance. Comparative genomics revealed conserved gene structure, with susceptible species exhibiting a higher number of SEO genes. Promoter analysis revealed an enrichment of light-responsive cis-elements in susceptible species, which is particularly interesting given the direct influence of light on HLB severity. Among these, we identified those exclusively present in susceptible species for further investigation. Moreover, we prospected a unique phloem-specific cis-element in the promoter of CsSEOc, a gene upregulated under HLB stress. Physicochemical characterization, subcellular localization, and phylogenetic analysis provided a comprehensive characterization of SEO family. Moreover, gene cooccurrence analysis and protein interaction networks revealed strong associations with Arabidopsis immune regulators associated to effector-triggered immunity, suggesting a broader role in defense beyond phloem blockage. These findings offer new insights into SEO-mediated immune responses, highlighting potential target genes and cis-elements for genome editing with no critical effects on phloem biology.