SERRALYSIN-LIKE PROTEIN OF CANDIDATUS LIBERIBACTER ASIATICUS AFECTS EXTRACELULAR MATRIX IN HETEROLOGOUS SYSTEMS AND VIRULENCE IN HOST PLANTS

MOLINA MARIA CELESTE; GARCÍA LUCILA; BRUNA ROBERTO; TORRES PABLO; GARCÍA VÉSCOVI ELEONORA; GONZALEZ CLAUDIO; GADEA JOSE; MARANO MARIA ROSA

Modalidad Virtual

Congreso; LVI SAIB MEETING; 2020

SAIB SAMIGE

Huanglongbing (HLB) is the major threat for Citrus species and it is caused by intracellular alfa-proteobacteria belong to thegenus Candidatus Liberibacter (CaL), being ´Ca. L. asiaticus´ (Las) the prevalent specie. This bacterium is psyllid-transmittedand resides within the citrus phloem. Infected trees symptoms -blotchy and mottled leaves, small fruits, as well as shorterlifespan and premature fruit drop- have been associated with an increase of callose deposition and starch accumulation thatconstricts symplastic transport producing a source-sink imbalance. The inability to culture CaL has hampered progress instudying the pathogen and its virulence mechanisms, our limited understanding relies on transcriptome and proteomic dataand on the expression of putative virulence proteins in surrogate models. Those studies highlight the idea that Las activelymanipulate plant defense response. Extracellular proteases which belong to the Serralysin metalloprotease family are wideknown virulence factors exported through the secretion system type I (SST1). A putative serralysin gene was identified in CaLgenomes and its expression levels was increased when Las changed it environment from the psyllid to the citrus leaf, suggestinga function in the infection process. Here, we study the function of the Las-serralysin (hereafter Las_1345) as virulence factor.First, we decipher whether Las_1345 could be secreted through bacteria that express SST1-secreted proteases such as Serratiamarcescens (Smc) and Xanthomonas citri and X. campestris (Xac and Xcc, respectively). Las_1345 only was detected in thepellet fraction of every surrogate bacteria, nevertheless, we measured intracellular protease activity. Las_1345 expressionincreased the proteolityc activity of Xcc by more than 50% and partially restored (5-10%) the protease activity of proteasedeficient Smc strain (prtA). Las_1345 purified from E. coli also showed low proteolytic activity. Then, we analyzed whetherLas_1345 can exert its activity on plant proteins. Las_1345-GFP was localized at the cell membrane in Nicotiana benthamianaand tissue integrity was not affected. Moreover, protease activity measured in tissue cells expressing Las_1345 arose similarlevels as in control tissue, suggesting that Las_1345 may not act as protease in plant tissue. Interesting, Las_1345 modifybiofilm structure in surrogate bacteria, which was associated with less virulence in citrus plants. We propose that Las_1345 isa virulence factor contributing with Las colonization in the citrus phloem.