Plant defense responses to biotic stresses are complex biological processes, all governed by sophisticated molecular regulations. Induced systemic resistance (ISR) is one of these defense mechanisms where beneficial bacteria or fungi prime plants to resist pathogens or pest attacks. In ISR, the defense arsenal in plants remains dormant and it is only triggered by an infection, allowing a better allocation of plant resources. Our group recently described that the well-known beneficial bacterium Paraburkholderia phytofirmans PsJN is able to induce Arabidopsis thaliana resistance to Pseudomonas syringae pv. tomato ( Pst ) DC3000 through ISR, and that ethylene, jasmonate and salicylic acid are involved in this protection. Nevertheless, the molecular networks governing this beneficial interaction remain unknown. To tackle this issue, we analyzed the temporal changes in the transcriptome of PsJN-inoculated plants before and after being infected with Pst DC3000. These data were used to perform a gene network analysis to identify highly connected transcription factors. Before the pathogen challenge, the strain PsJN regulated 405 genes (corresponding to 1.8% of the analyzed genome). PsJN-inoculated plants presented a faster and stronger transcriptional response at 1-hour post infection (hpi) compared with the non-inoculated plants, which presented the highest transcriptional changes at 24 hpi. A principal component analysis showed that PsJN-induced plant responses to the pathogen could be differentiated from those induced by the pathogen itself. Forty-eight transcription factors were regulated by PsJN at 1 hpi, and a system biology analysis revealed a network with four clusters. Within these clusters LHY, WRKY28, MYB31 and RRTF1 are highly connected transcription factors, which could act as hub regulators in this interaction. Concordantly with our previous results, these clusters are related to jasmonate, ethylene, salicylic, acid and ROS pathways. These results indicate that a rapid and specific response of PsJN-inoculated plants to the virulent DC3000 strain could be the pivotal element in the protection mechanism.

Laternula elliptica is a key bivalve species and widely distributed around the Antarctic continent. This bivalve has been the study subject in several studies centered on ecological, physiological, biochemical, and behavioral patterns. However, little is known about the chemistry and the biomechanical properties of the shells of this mollusk. Here, we present the first report of the intra-population variability in the organic composition and mechanical properties of L. elliptica shells. Further, we analyze different morphological traits and their association with the metabolism of a population of L. elliptica from King George Island, Western Antarctic Peninsula. The summer metabolic rates and the hepatosomatic index values indicate good health conditions of this clam's population. Shell periostracum chemistry is quite similar to bivalves from temperate regions, but the relative amount of protein increased ca. five-fold in shells of L. elliptica. The microhardness is approximately 32% lower than in bivalves from temperate regions. Our characterization of the L. elliptica shells suggests that periostracum chemistry could be specially fitted to avoid shell carbon exposure to dissolution (e.g., in corrosive acidified seawater). In contrast, the reduction in shell hardness may result from prioritizing behavioral (burial) and shell repairing strategies to confront biological (predators) and physical disturbances (e.g., ice scouring). Similar studies in other Antarctic mollusks will help understand the role of shell structure and function in confronting projected climate changes in the Antarctic ocean.