KNOX1 Transcription Factors in Plants with a Special Focus on Horticultural Crops: A Review

Class I KNOX1 (KNOTTED1-like homeobox 1) transcription factors integrate gibberellin (GA), cytokinin (CK), and auxin (IAA) signaling to maintain shoot apical meristem identity and coordinate plant organogenesis. This review examines the structural conservation, evolutionary dynamics, and regulatory architecture of KNOX1 genes across horticultural crops, drawing essential mechanistic context from model species. We synthesize KNOX1 functions in six agronomic domains, including plant architecture and branching, leaf morphogenesis and ornamental traits, floral development and sex determination, fruit formation and quality, storage organ specification, and abiotic stress resilience. Particular attention is given to recent breakthroughs in cucurbit inferior ovary development, tomato chloroplast patterning, and potato tuber morphogenesis. We identify critical bottlenecks constraining translation, including fragmented regulatory networks, recalcitrant transformation systems in woody perennials, uneven taxonomic coverage favoring annual vegetables over ornamentals and medicinal species, and a near-complete absence of multi-environment field validation. We propose four strategic priorities to bridge this gap: (i) construction of spatiotemporal expression atlases using single-cell and spatial transcriptomics; (ii) tissue-specific and promoter-engineered CRISPR/Cas9 editing to circumvent pleiotropic penalties; (iii) cross-species comparative evo-devo analysis of lineage-specific innovations (compound leaves, inferior ovaries, tubers); and (iv) integrated field trials assessing genotype-by-environment interactions and trait stability. This framework aims to accelerate KNOX1-directed molecular design breeding in horticultural crops.