2018 ASHS Annual Conference

In plants, the long-distance movement of photosynthates, defense compounds, and signals essential for plant growth and development occurs via the phloem vascular tissue. The phloem is also a key route for the spread of plant pathogens. However, how phloem transport functions at the cellular and molecular levels has been a challenging question to address in part due to the technical difficulty of sampling phloem tissues. The phloem is a pressurized system, and disruption of this pressurized system as is done in many phloem sampling techniques can lead to damage and the introduction of components from neighboring cells. In this study, we adapted a new phloem specific sampling method, called translating ribosome affinity purification (TRAP), for use in plum trees (Prunus domestica L). An advantage of this approach is that it does not require disruption of the pressurized phloem system prior to mRNA harvesting. Using this method, we identified 1100 genes that were specifically active in the phloem and characterized their activities over the course of leaf development. We found that up regulated genes were involved in nutrient metabolism, defense responses, and reproduction. While down regulated genes were largely associated with DNA replication. The results reveal new insights into leaf and phloem development and establish TRAP as a powerful tool for studying tissue specific functions and responses in trees.