Expression of genes encoding sucrose synthase isoforms during anomalous xylogenesis in Karelian birch

Abstract

Activity of sucrose synthase (SS) and the transcript levels for SS-encoding genes SUS1, SUS2, and SUS3 were assayed during xylogenesis in two varieties of silver birch: common birch (Betula pendula Roth var. pendula) and Karelian birch (B. pendula var. carelica (Mercklin)). The xylem specimens of Karelian birch were sampled from the trunks with the “normal” wood structure (unpatterned trees) and from the trunks of patterned trees in stem regions exhibiting patterned and unpatterned wood. In the period of high cambial activity, the SS activity in common silver birch was elevated due to expression of SuSy1 isoform (SUS1 gene). The UDP-glucose produced in these trees was largely used for cellulose synthesis in cell walls of conducting vessels and fibers that are the main wood constituents in these plants. In Karelian birch, the patterned wood with abundant parenchymal cells was formed on the background of a substantial decrease in expression of SUS1 and SUS2 genes, inhibition of SS activity, and lowering the cellulose content per unit tissue weight. Within the same trees of Karelian birch, the unpatterned wood regions containing numerous conducting vessels and fibers were formed on the background of high expression of SUS1 and SUS2 genes, elevated SS activity, and substantial accumulation of cellulose and starch. The unpatterned plants of Karelian birch occupied intermediate position in terms of SS activity and cellulose content between the common birch and Karelian birch trees with the patterned wood. The results shed new light on the role of SS in the induction of structural anomalies in the wood of Karelian birch.