Transcriptome profiling in Salix matsudana during refilling xylem vessels after embolism

Abstract

The objective of this study is to understand the role of bark water uptake in refilling of xylem vessels after embolism in Salix matsudana. Further, we determined expression of genes closely related to xylem embolism repair. The isolated branch segments of S. matsudana were soaked in deionized water and after 2 h, the micro-computed tomography (CT) images, volume of xylem sap, osmotic potential of xylem sap, and the content of starch and soluble sugar were measured. At the same time, Illumina high-throughput sequencing (Hi Seq TM) was applied to obtain the xylem transcriptome profiling. The results showed that the soaked branches had 58.86 % fewer embolized vessels than branches before soaking. The volume of xylem sap was increased by 21.51 % in comparison with initial sample and the osmotic potential (Ψs) of xylem sap was decreased by 87.18 %. The content of ions and soluble sugars in the xylem sap significantly increased after soaking. Fourteen genes were clarified and found to have a significant correlation with osmotic potential of xylem sap. Our findings showed that water can enter the xylem vessels through the bark and can repair the xylem embolism in branches. The saccharides played an important role in osmotic potential difference formation and the genes UXL1 (uridine diphosphate-xylose synthase 1), UGDH (uridine diphosphate-glucose 6-dehydrogenase), BGLU40 (β-glucosidase 40), PPE8B (pectinesterase/pectinesterase inhibitor), UG1 (uridine diphosphate-glucuronate 1), and XYL4 (β-D-xylosidase 4)) were the key genes to promote embolized vessels refilling.

Keywords

• bark water uptake
• embolism repair
• micro-computed tomography
• osmotic potential
• soluble sugars