Abstract:
In this study, we examine the impact of transcriptional network rearrangements
driven by horizontal gene acquisition in PhoP and SlyA regulons using
as a case study a phytopathosystem comprised of potato tubers and the soft-rot
pathogen Pectobacterium brasiliense 1692 (Pb1692). Genome simulations and statistical
analyses uncovered the tendency of PhoP and SlyA networks to mobilize
lineage-specific traits predicted as horizontal gene transfer at late infection, highlighting
the prominence of regulatory network rearrangements in this stage of infection.
The evidence further supports the circumscription of two horizontally acquired
quorum-sensing regulators (carR and expR1) by the PhoP network. By recruiting carR
and expR1, the PhoP network also impacts certain host adaptation- and bacterial
competition-related systems, seemingly in a quorum sensing-dependent manner,
such as the type VI secretion system, carbapenem biosynthesis, and plant cell walldegrading
enzymes (PCWDE) like cellulases and pectate lyases. Conversely, polygalacturonases
and the type III secretion system (T3SS) exhibit a transcriptional pattern
that suggests quorum-sensing-independent regulation by the PhoP network. This includes
an uncharacterized novel phage-related gene family within the T3SS gene
cluster that has been recently acquired by two Pectobacterium species. The evidence
further suggests a PhoP-dependent regulation of carbapenem- and PCWDE-encoding
genes based on the synthesized products’ optimum pH. The PhoP network also controls
slyA expression in planta, which seems to impact carbohydrate metabolism regulation,
especially at early infection, when 76.2% of the SlyA-regulated genes from
that category also require PhoP to achieve normal expression levels.
