article
A serralysin-like protein of Candidatus Liberibacter asiaticus modulates components of the bacterial extracellular matrix
Autor
García, Lucila
Molina, María Celeste
Padgett Pagliai, Kaylie Allyson
Torres, Pablo S.
Bruna, Roberto Emanuel
García Véscovi, Eleonora
González, Claudio F.
Gadea, José
Marano, María Rosa
Institución
Resumen
Huanglongbing (HLB), the current major threat for Citrus species, is caused by
intracellular alphaproteobacteria of the genus Candidatus Liberibacter (CaL),
with CaL asiaticus (CLas) being the most prevalent species. This bacterium
inhabits phloem cells and is transmitted by the psyllid Diaphorina citri. A gene
encoding a putative serralysin-like metalloprotease (CLIBASIA_01345) was
identified in the CLas genome. The expression levels of this gene were found
to be higher in citrus leaves than in psyllids, suggesting a function for this
protease in adaptation to the plant environment. Here, we study the putative
role of CLas-serralysin (Las1345) as virulence factor. We first assayed whether
Las1345 could be secreted by two different surrogate bacteria, Rhizobium
leguminosarum bv. viciae A34 (A34) and Serratia marcescens. The protein was
detected only in the cellular fraction of A34 and S. marcescens expressing
Las1345, and increased protease activity of those bacteria by 2.55 and 4.25-
fold, respectively. In contrast, Las1345 expressed in Nicotiana benthamiana
leaves did not show protease activity nor alterations in the cell membrane,
suggesting that Las1345 do not function as a protease in the plant cell. Las1345
expression negatively regulated cell motility, exopolysaccharide production,
and biofilm formation in Xanthomonas campestris pv. campestris (Xcc). This
bacterial phenotype was correlated with reduced growth and survival on
leaf surfaces as well as reduced disease symptoms in N. benthamiana and
Arabidopsis. These results support a model where Las1345 could modify
extracellular components to adapt bacterial shape and appendages to the
phloem environment, thus contributing to virulence.