Transcriptomic analysis of tomato plants subjected to multifactorial stress combination

Climate change and industrial pollution are responsible for major losses in crop yield worldwide. Tomato plants are subjected to multiple stress conditions in combination when growing in the natural field. In this work, we analyzed the transcriptomic response of tomato plants to the combination of salinity and heat stress, when plants were or were not inoculated with the beneficial bacteria Pseudomonas Putida. The results suggest that specific transcripts are regulated only under stress combination in plants inoculated with the bacteria. These transcripts could be related with the enhanced tolerance of inoculated plants under conditions of stress combination. Moneymaker tomato plants were grown in seedling trays filled with peat moss, perlite, and vermiculite (80:10:10). After germination, seedlings were transplanted to 10-cm diameter pots filled with a mix of sterile autoclaved peat moss and perlite (2:1) and maintained under greenhouse conditions (70% relative humidity, 200 µmol photons m-2· s-1 light intensity, natural photoperiod day/night cycle with temperatures averaging 25.0°C and 18.0°C, respectively). 3-week-old plants were inoculated with Pseudomonas putida KT2240 (OD660 =0.05) through the roots and the rest of the plants were watered with the same amount of M8 buffer 10 days before starting stress treatments. Then, plants were subjected to four different conditions: control (CT), heat stress (37ºC; HS), salinity (150 mM NaCl; S), and the combination of salinity and heat stress (150 mM NaCl + 37ºC; S+HS). Plants were watered three times a week for 15 days with Hoagland solution or salinity stressor in a half-strength Hoagland solution. For stress combinations that included HS, plants watered in the presence or absence of salinity were subjected to a 3-day treatment of HS (37ºC) in growth chambers. Therefore, eight experimental groups were designed (CT, Pp, HS, HS+Pp, S, S+Pp, HS+S, HS+S+Pp).