The Lateral Organ Boundaries Domain Transcription Factor LBD20 Functions in Fusarium Wilt Susceptibility and Jasmonate Signaling in Arabidopsis  

Abstract

The LATERAL ORGAN BOUNDARIES (LOB) DOMAIN (LBD) gene family encodes plant-specific transcriptional regulators functioning in organ development. In a screen of Arabidopsis (Arabidopsis thaliana) sequence-indexed transferred DNA insertion mutants, we found disruption of the LOB DOMAIN-CONTAINING PROTEIN20 (LBD20) gene led to increased resistance to the root-infecting vascular wilt pathogen Fusarium oxysporum. In wild-type plants, LBD20 transcripts were barely detectable in leaves but abundant in roots, where they were further induced after F. oxysporum inoculation or methyl jasmonate treatment. Induction of LBD20 expression in roots was abolished in coronatine insensitive1 (coi1) and myc2 (allelic to jasmonate insensitive1) mutants, suggesting LBD20 may function in jasmonate (JA) signaling. Consistent with this, expression of the JA-regulated THIONIN2.1 (Thi2.1) and VEGETATIVE STORAGE PROTEIN2 (VSP2) genes were up-regulated in shoots of lbd20 following treatment of roots with F. oxysporum or methyl jasmonate. However, PLANT DEFENSIN1.2 expression was unaltered, indicating a repressor role for LBD20 in a branch of the JA-signaling pathway. Plants overexpressing LBD20 (LBD20-OX) had reduced Thi2.1 and VSP2 expression. There was a significant correlation between increased LBD20 expression in the LBD20-OX lines with both Thi2.1 and VSP2 repression, and reduced survival following F. oxysporum infection. Chlorosis resulting from application of F. oxysporum culture filtrate was also reduced in lbd20 leaves relative to the wild type. Taken together, LBD20 is a F. oxysporum susceptibility gene that appears to regulate components of JA signaling downstream of COI1 and MYC2 that are required for full elicitation of F. oxysporum-and JA-dependent responses. To our knowledge, this is the first demonstration of a role for a LBD gene family member in either biotic stress or JA signaling.

Lateral organ boundaries 1 is a disease susceptibility gene for citrus bacterial canker disease

“…One member of the LOB domain family, AtLBD18, was reported to bind with the promoter of EXPANSIN14, a gene involved in cell wall loosening (38). Recently, the Arabidopsis LOB family protein LBD20 was proposed as a host S gene for the fungal pathogen Fusarium oxysporum, functioning in the jasmonate signaling pathway (39). AtLBD20 was induced by F. oxysporum, and the overexpression of LBD20 was correlated with increased susceptibility to infection and reduced the expression of JA-regulated genes VEGETATIVE STORAGE PROTEIN2 (VSP2) and THI-ONIN2.1 (Thi2.1).…”

Plant defense response against Fusarium oxysporum and strategies to develop tolerant genotypes in banana

“…Thatcher et al (2009), have demonstrated JA perception mutant coronatine insensitive 1 (coi1), but not JA biosynthesis mutants, which exhibited a high level of resistance to wilt disease caused by F. oxysporum in Arabidopsis Kidd et al (2011) thaliana. Recently a novel transcription factor, LBD20 (Lateral Organ Boundaries Domain) gene which on its disruption led to increased resistance in Arabidopsis to Fox was found and this suggests that LBD20 is a Fusarium susceptibility gene that appears to regulate components of JA-signaling downstream of COI1 and MYC2 transcription factors (Thatcher et al 2012a). JA signaling has a dichotomous involvement in the Arabidopsis interaction with F. graminearum, contributing to the attenuation of SA signaling during the early stages of infection and promotion of defense against F. graminearum during later stages of infection (Makandar et al 2010).…”

Lateral organ boundaries domain transcription factors

“…In addition to LBD20 expression being induced by F. oxysporum infection, we also found its expression was responsive to the defense signaling hormone JA. 15 In GENEVESTIGATOR, we only found LBD genes differentially expressed greater than 1.5-fold from controls to be repressed by JA treatment (data not shown). Again, the class II LBD genes (LBD37, 38, 39 and 41) were most responsive.…”

“…14, [16][17][18] We now demonstrate a role for LBD20 in JA-signaling where it functions downstream of COI1 and MYC2, 15 respectively part of the JA receptor complex and a key downstream transcriptional regulator of JA signaling (for a review see ref. 19).…”

“…We found LBD20 functions as a repressor of a subset of JA-regulated defense genes however, it is not known whether LBD20 directly or indirectly represses their transcription. 15 Unlike class I LBD proteins, those characterized so far function of most LBD family members is not known, although diverse functions have been proposed for those characterized to some extent. These roles include regulating organ development, anthocyanin or nitrogen metabolism, or responses to phytohormones such as cytokinin, auxin and gibberellins.…”