Identification of WAT1-like genes in Panax ginseng and functional analysis in secondary growth

The precise homeostatic regulation of local auxin accumulation in xylem precursors of cambium stem cell tissues is one of the most important mechanisms for plant vascular patterning and radial secondary growth. Walls are thin (WAT1), a novel intracellular auxin transporter, contributes directly to the auxin accumulation maxima in xylem precursors. According to recent research, the auxin signaling activated pathway-related gene network was significantly enriched during the secondary growth of Panax ginseng storage roots. These imply that during P. ginseng root secondary growth, specific signaling mechanisms for local auxin maxima in the vascular cambial cells are probably triggered. This study identified four WAT1-like genes, PgWAT1-1/-2 and PgWAT2-1/-2, in the P. ginseng genome. Their expression levels were greatly increased in nitratetreated storage roots stimulated for secondary root growth. PgWAT1-1 and PgWAT2-1 were similar to WAT1 from Arabidopsis and tomato plants in terms of their subcellular localization at a tonoplast and predicted transmembrane topology. We discovered that overexpression of PgWAT1-1 and PgWAT2-1 was sufficient to compensate for the secondary growth defects observed in slwat1-copi loss of function tomato mutants. This critical information from the PgWAT1-1 and PgWAT2-1 genes can potentially be used in future P. ginseng genetic engineering and breeding for increased crop yield.