Transcriptomic analysis of wrinkled leaf development of Tai-cai (Brassica rapa var. tai-tsai) and its synthetic allotetraploid via RNA and miRNA sequencing.

The allotetraploid (AACC) was synthesized through wide hybridization between 'Mottle-leaf Tai-cai' (Brassica rapa var. tai-tsai Hort. AA) and 'Big Yellow Flower Chinese Kale' (B. oleracea var. alboglabra Bailey. CC) in earlier study, which owns a stronger wrinkled leaf and wave margin than Tai-cai. To analyze the structure and developmental mechanism of wrinkled leaf and wave edge, four leaf development stages were chosen for RNA-seq and their key stages for anatomical observation. As a result, the number of cell layers and compactness of AA and AACC were significantly increased in folded parts, and the enlargement of epidermal cells causes the leaf edge to curve inward. The gene expression bias of AACC showed no difference in the cotyledon stage, favored the A genome in the first leaf stage, however, favored the C genome in the third leaf and fifth leaf stages, showing an expression level advantage over the C genome parent. During the leaf development, the plant hormone signaling pathway were significantly enriched, PIN1 (BraC07g037600), AUX1 (BraC05g007870), AUX/IAA (BraC03g037630), and GH3 (BraC10g026970), which maintained high expression during the euphylla leaf stage of AA and AACC. And these genes performed different patterns in CC. In addition, the expression levels of miR319 and miR156 of AA were significantly higher than those of CC, and the expression levels of their target genes TCP and SPL were lower. These genes were jointly involved in the development of AA and AACC leaves and may be closely related to the formation of leaf folds and waves.