|Collum, Tamara - Tami
|Raines, Charles - Doug
|Dardick, Christopher - Chris
|CULVER, JAMES - University Of Maryland
Submitted to: Horticulture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2018
Publication Date: 2/1/2019
Citation: Collum, T.D., Lutton, E., Raines, C.D., Dardick, C.D., Culver, J. 2019. Identification of phloem-associated translatome alterations during leaf development in Prunus domestica L. Horticulture Research. 6:16. https://doi.org/10.1038/s41438-018-0092-4
Interpretive Summary: Plants, like animals, have vascular systems to move nutrients, hormones, and other molecules essential for growth and development over long distances. Water and minerals from the soil are taken up and moved through columns of dead cells called xylem. In contrast, the phloem is composed of columns of living cells situated next to the xylem that can move molecules both up and down the plant through stems, leaves, and roots. Despite the importance of the phloem in plant biology there is little known about how it functions at the cellular and molecular levels. This is in part, due to the technical difficulty of sampling phloem tissues. In this study we adapted a new phloem sampling method, called translating ribosome affinity purification (TRAP), for use in plum trees. 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 phloem specific functions and responses in trees. The tools and knowledge gained will have wide ranging impacts on the study of woody plants and trees.
Technical Abstract: Phloem plays a fundamental role in plants by transporting hormones, nutrients, proteins, RNAs, and carbohydrates essential for plant growth and development. However, the identity of the underlying phloem genes and pathways remain enigmatic especially in agriculturally important perennial crops, in part, due to the technical difficulty of phloem sampling. Here, we used two phloem specific promoters and a translating ribosome affinity purification (TRAP) strategy to characterize the phloem translatome during leaf development at two, four and six weeks post vernalization in plum (Prunus domestica L). Results provide insight into the changing phloem processes that occur during leaf development. These processes included the early activation of DNA replication genes that are likely involved in phloem cell division during leaf expansion as well as the up regulation of phloem genes associated with sink to source conversion, induction of defense processes and signaling for reproduction. Combined these results reveal the dynamics of phloem gene expression during leaf development and establish the TRAP system as a powerful tool for studying phloem specific functions and responses in trees.