Position-specific transcriptomic and microRNA profiles reveal candidate regulatory modules associated with leaf curvature and leafy head formation in cabbage ( Brassica oleracea var.

Abstract

Leaf curvature is a key developmental process in leafy head formation of cabbage (Brassica oleracea var. capitata), yet the molecular and physiological mechanisms coordinating this morphogenesis remain poorly understood. Previous anatomical analyses showed that differential growth across the leaf blade and between adaxial and abaxial mesophyll tissues is associated with leaf curvature. Here, we investigated mRNA and microRNA abundance profiles across four defined leaf positions in flat rosette and curved heading leaves from round- and pointed cabbage genotypes. Comparative profiling of heading leaves revealed significant position-dependent transcriptional divergence in transcript abundance, with the mid and base leaf positions (central regions) distinct from the tip and lateral leaf positions (marginal regions), which was not the case in rosette leaves. Heading leaves displayed substantially more differentially expressed genes (DEGs) than rosette leaves, indicating enhanced transcriptional differentiation during head formation. Functional enrichment analyses of these positional DEGs highlighted growth- and morphogenesis-related differences between central and marginal regions, involving genes associated with hormone regulation, cell division, and cytoskeleton organization. Integrative correlation analysis identified 14 candidate miRNA–gene modules with position-dependent inverse expression patterns, including miR396–BoGRFs, miR166–BoREVs, miR167–BoARFs, and miR6031–BoKAN2, whose predicted targets are associated with leaf growth and polarity. Together, these results reveal position-dependent mRNA and microRNA expression patterns associated with differential leaf growth and curvature, and provide candidate regulatory modules for future functional studies of leafy head formation and head shape variation in Brassica crops.