The Formation of Structural Abnormalities in Karelian Birch Wood is Associated with Auxin Inactivation and Disrupted Basipetal Auxin Transport

Expression Analysis of Key Auxin Biosynthesis, Transport, and Metabolism Genes of Betula pendula with Special Emphasis on Figured Wood Formation in Karelian Birch

“…We investigated the expression of eight Yucca genes and nine GH3 genes identified within this study, as well as six PIN genes and two UGT genes identified in the silver birch genome previously [ 69 ]. The analysis revealed no expression of the Bpev01.c0015cg0065 gene coding for one of the two putative IAA–glucose synthases in any of the studied tissues.…”

“…It has previously been demonstrated that, after many years of figured wood formation in adult Karelian birch trees (25–30-year-old), the vessel density in the anomaly areas is much lower than in the wood of common silver birch, while, in non-figured parts, vessel density is slightly lower [ 58 , 59 , 69 ]. Analysis of auxin content revealed a reduction in the concentration of free auxin and a rise in the concentration of auxin conjugates in the areas of anomalies [ 64 ], thus supporting the evidence that the development of anomalous conducting tissues in Karelian birch trunks is closely associated with auxin inactivation.…”

“…It is in early development stages that Karelian birch saplings feature a more active carbohydrate metabolism compared to common silver birch [ 97 , 98 ]. It has been demonstrated for trees of different ages that figured wood formation in Karelian birch is associated with a rise in the amount of photoassimilates transported via the phloem and with high hexose influx to cells in the differentiating xylem [ 58 , 63 , 67 , 69 ]. It can thus be concluded that an altered metabolic status of differentiating trunk tissues is strong biochemical marker of abnormal xylogenesis.…”

“…Research into biochemical aspects revealed that figured wood in Karelian birch forms in the context of a reduced level of free (physiologically active) auxin and a high concentration of sucrose in trunk tissues, which is degraded involving cell wall invertase, while birch trees forming wood typical of the species have a higher auxin level, and sucrose in their trunk tissues is primarily metabolised by sucrose synthase [ 58 , 63 , 64 , 65 , 66 , 67 , 68 ]. The molecular groundwork of interactions between auxin and sugars in the process of anomalous wood formation in Karelian birch, however, has so far been studied very little [ 69 ]. Meanwhile, such studies are of high theoretical as well as practical interest, since variants of abnormal xylogenesis occur in a number of other woody plants, too.…”

“…A hypothesis has recently been proposed that figured wood formation in Karelian birch may have to do with inactivation of free auxin as a result of auxin conjugation which, via a chain of biochemical reactions, may be associated with hexoses produced in the apoplast through sucrose cleavage by cell wall invertase [ 69 ]. We know, however, that sugars can modulate auxin metabolism and transport both by acting as substrates in conjugation reactions and by regulating gene expression [ 39 , 76 , 77 , 78 ].…”