IDENTIFICATION OF CANDIDATE GRF AND MIR396 REGULATOR GENES IN POPLARS INVOLVED IN RESPONSE TO ABIOTIC STRESSES

Every year, acres of crop plants are lost to unsuitable conditions brought on by abiotic stressors. To combat this loss, researchers around the world aim to understand the molecular mechanisms required for tolerance to such conditions. In this search, many plants have been shown to utilize conserved regulatory gene families such as growth regulating factors (GRFs) and microRNA-396 (miR396). Typically, GRFs and miR396 form a regulatory balance, with GRFs promoting cell growth, expansion, and development, while miR396 targeting GRF transcripts for degradation. Shifts in this dynamic have been linked to stress responses and tolerance mechanisms in a variety of plants, though they have not yet been characterized in tree species. Here, we aimed to utilize Populus trichocarpa (poplar), a common bioenergy tree and model organism, to identify key characteristics and candidate regulatory elements of the poplar GRF-miR396 stress responses in cold, heat, drought, and salt stress conditions. We found each stress condition warrants a unique expression landscape in GRF and miR396 genes, often in a tissue- and duration-specific manner. Across the conditions tested GRF01, GRF03, GRF07, GRF11, GRF12, GRF16, GRF17, pri-miR396b, and pri-miR396e are repeatedly differentially expressed, with GRF12 and GRF17 alongside the pri-miR396 genes being the most prominent. We find GRF and pri-miR396 expression correlates in parallel, unlike other plants, which insinuates there are other regulatory genes affecting the pathway, either inhibiting the transition from pri-miR396 to mature miR396 or acting as a negative regulator toward GRFs of which has a higher binding affinity with miR396. The latter has been previously documented in poplar and is more plausible