Additive roles of PthAs in bacterial growth and pathogenicity associated with nucleotide polymorphisms in effector-binding elements of citrus canker susceptibility genes

Author(s)

Abe, Valeria Yukari ; Benedetti, Celso Eduardo

• Document type: Journal article
• Source: MOLECULAR PLANT PATHOLOGY; v. 17, n. 8, p. 1223-1236, OCT 2016.
• Web of Science Citations: 7

Abstract

Citrus canker, caused by Xanthomonas citri, affects most commercial citrus varieties. All X. citri strains possess at least one transcription activator-like effector of the PthA family that activates host disease susceptibility (S) genes. The X. citri strain 306 encodes four PthA effectors; nevertheless, only PthA4 is known to elicit cankers on citrus. As none of the PthAs act as avirulence factors on citrus, we hypothesized that PthAs 1-3 might also contribute to pathogenicity on certain hosts. Here, we show that, although PthA4 is indispensable for canker formation in six Brazilian citrus varieties, PthAs 1 and 3 contribute to canker development in Pera' sweet orange, but not in Tahiti' lemon. Deletions in two or more pthA genes reduce bacterial growth in planta more pronouncedly than single deletions, suggesting an additive role of PthAs in pathogenicity and bacterial fitness. The contribution of PthAs 1 and 3 in canker formation in Pera' plants does not correlate with the activation of the canker S gene, LOB1 (LATERAL ORGAN BOUNDARIES 1), but with the induction of other PthA targets, including LOB2 and citrus dioxygenase (DIOX). LOB1, LOB2 and DIOX show differential PthA-dependent expression between Pera' and Tahiti' plants that appears to be associated with nucleotide polymorphisms found at or near PthA-binding sites. We also present evidence that LOB1 activation alone is not sufficient to elicit cankers on citrus, and that DIOX acts as a canker S gene in Pera', but not Tahiti', plants. Our results suggest that the activation of multiple S genes, such as LOB1 and DIOX, is necessary for full canker development. (AU)

• FAPESP's process: 11/19988-0 - Functional analysis of the TAL effectors from Xanthomonas citri and Xanthomonas aurantifolii patotipo C
• Grantee: Valeria Yukari Abe
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 11/20468-1 - Molecular mechanisms involved in pathogen adaptation and virulence, host resistance and symptom development in citrus-bacteria interactions
• Grantee: Celso Eduardo Benedetti
• Support Opportunities: Research Projects - Thematic Grants