Genetic mapping of the dominant gene controlling weeping habit in Japanese chestnut (Castanea crenata Sieb. et Zucc.)

Abstract

Trees with weeping traits have been prized for centuries because of their unique shape. Weeping trees of various species have been selected and propagated for their ornamental appeal as landscape plants, but there is limited information on the genes that control weeping. The genetic control of weeping in Japanese chestnut (Castanea crenata Sieb. et Zucc.) is reported to involve a dominant or recessive gene depending on the genetic background. In every case examined to date, weeping is controlled by a single gene of unknown location. Here, we identified the exact position of the dominant gene controlling the weeping trait in the Japanese chestnut. Using the genome scanning approach, which can cost-effectively screen for markers linked to traits, we first mapped this gene, referred to here as Weep, to the middle of linkage group L. Then, we developed new simple sequence repeat (SSR) markers using the genomic resources to enrich the target region. Using these markers and previously reported markers, we constructed the linkage group covering most of the chromosome (60.9 cM) with an average marker density of 4.7 cM per marker. Weep was located within a 3.0-cM genome region. SSR marker CmSca01437 co-segregated with Weep in all 138 F1 plantlets of a Tsukuba-38 × 668-6 cross. Our identification of the exact locus of the dominant weeping gene in Japanese chestnut, in conjunction with previous studies of recessive weeping genes in this and other tree species, furthers our understanding of the genetic mechanism of the weeping trait.