The Expansin Gene CsLIEXP1 Is a Direct Target of CsLOB1 in Citrus

Author(s)

de Souza-Neto, Reinaldo Rodrigues ; da Costa Vasconcelos, Fernanda Nogales ; Teper, Doron ; Barbosa Carvalho, Isis Gabriela ; Takita, Marco Aurelio ; Benedetti, Celso Eduardo ; Wang, Nian ; de Souza, Alessandra Alves

• Document type: Journal article
• Source: PHYTOPATHOLOGY; v. 113, n. 7, p. 12-pg., 2023-07-01.

Abstract

Transcription activator-like effectors are key virulence factors of Xanthomonas. They are secreted into host plant cells and mimic transcription factors inducing the expression of host susceptibility (S) genes. In citrus, CsLOB1 is a direct target of PthA4, the primary effector associated with citrus canker symptoms. CsLOB1 is a transcription factor, and its expression is required for canker symptoms induced by Xanthomonas citri subsp. citri. Several genes are up-regulated by PthA4; however, only CsLOB1 was described as an S gene induced by PthA4. Here, we investigated whether other up-regulated genes could be direct targets of PthA4 or CsLOB1. Seven up-regulated genes by PthA4 were investigated; however, an expansin-coding gene was more induced than CsLOB1. In Nicotiana benthamiana transient expression experiments, we demonstrate that the expansin-coding gene, referred here to as CsLOB1-INDUCED EXPANSIN 1 (CsLIEXP1), is not a direct target of PthA4, but CsLOB1. Interestingly, CsLIEXP1 was induced by CsLOB1 even without the predicted CsLOB1 binding site, which suggested that CsLOB1 has other unknown binding sites. We also investigated the minimum promoter regulated by CsLOB1, and this region and LOB1 domain were conserved among citrus species and relatives, which suggests that the interaction PthA4-CsLOB1-CsLIEXP1 is conserved in citrus species and relatives. This is the first study that experimentally demonstrated a CsLOB1 downstream target and lays the foundation to identify other new targets. In addition, we demonstrated that the CsLIEXP1 is a putative S gene indirectly induced by PthA4, which may serve as the target for genome editing to generate citrus canker-resistant varieties. (AU)

• FAPESP's process: 17/13885-1 - Use of CRISPR/Cas9 in the editing of susceptibility genes of citrus sinensis to Xanthomonas citri subsp. Citri
• Grantee: Reinaldo Rodrigues de Souza Neto
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 18/21990-2 - Use of CRISPR-Cas9 to edit citrus canker susceptibility genes to obtain commercial sweet orange varieties resistant to Xanthomonas citri subsp. citri
• Grantee: Reinaldo Rodrigues de Souza Neto
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 20/04795-1 - Transformation of sweet orange varieties for functional study and / or gene editing for resistance to citrus bacterial diseases
• Grantee: Isis Gabriela Barbosa Carvalho
• Support Opportunities: Scholarships in Brazil - Technical Training Program - Technical Training
• FAPESP's process: 13/10957-0 - Xylella fastidiosa-vector-host plant interaction and approaches for citrus variegated chlorosis and citrus canker control
• Grantee: Alessandra Alves de Souza
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 14/50880-0 - INCT 2014: comparative and functional genomics and citrus-assisted breeding
• Grantee: Marcos Antonio Machado
• Support Opportunities: Research Projects - Thematic Grants