CovQTL mapping reveals genetic mechanisms of competitive and cooperative growth between stem and leaf in Catalpa bungei

The cooperative and competitive relationships between dynamic growth (plant growth height) and static (stem- or leaf-related traits) traits affect photosynthetic efficiency. However, the underlying genetic mechanisms remain poorly understood. In this study, we applied covariation quantitative trait loci (covQTL) mapping to investigate the genetic regulation of the covariation pattern between dynamic growth in height (GH) and static leaf- or stem-related radial growth traits in Catalpa bungei . Our results revealed that leaf area, length, width, perimeter, and chlorophyll content positively influence GH, reflecting cooperative genetic interactions, while the leaf length/width ratio, diameter at breast height, and petiole length act as limiting factors for GH, indicating competitive genetic regulation. Furthermore, we identified 85 cooperation QTLs (CoopQTLs) and 27 competition QTL (CompQTLs), revealing key genes with distinct roles. NAC083 , a cooperation gene, regulates both plant height (GH) and leaf development by promoting cell expansion and division, through its involvement in cell wall biosynthesis and cell cycle regulation, as well as interactions with growth-related pathways like auxin and cytokinin signaling. In contrast, PIN8 , a competition gene, promotes GH by regulating auxin transport, directing auxin flow to promote stem elongation. However, it inhibits leaf vein elongation, especially the midrib, by disrupting auxin distribution in the leaf, leading to reduced leaf length. PIN8 and NAC083 were identified as hub genes within distinct genetic networks through gene expression analysis, further validating the modular regulation of competition and cooperation phenotypes by separate regulatory strategies. We highlight genetic mechanisms underlying stem-leaf growth coordination and trade-offs, providing valuable insights into the cooperative and competitive patterns in primary and leaf/stem-related growth for breeding forest tree varieties with optimal architecture, wood yield, and quality. Categorize eight dynamic-static phenotype pairs into cooperation and competition groups to reveal covariation patterns. Employ a covariation mapping model to identify cooperation QTLs (CoopQTLs) and competition QTL (CompQTLs), respectively. Verify key candidate genes using genotypic variation analysis, gene expression profiling, and regulatory network construction. The key cooperation gene, NAC083 , which positively regulates both dynamic GH and leaf growth and the key competition gene. The key competition gene, PIN8 , which promotes dynamic GH while competitively reducing leaf length.