<i>NtDEAH1</i> Modulates Gibberellin Receptor <i>NtGID1</i> Expression and Negatively Regulates Leaf Number in Tobacco

Tobacco (Nicotiana tabacum L.) is a crop of major economic importance worldwide and also a widely used model in plant biology and genetics. Leaf number (LN) is a key agronomic trait that determines yield. To elucidate its genetic basis, we developed a mapping population by crossing the low-leaf, high-quality cultivar 'NC82' with the high-leaf cultivar 'Jiucaiping No.2' (JCP2). Bulked segregant analysis initially placed the locus controlling LN within a 6.16 Mb region on chromosome 9. The integration of competitive allele-specific PCR markers with RNA sequencing data narrowed down this region and identified a single candidate gene, NtDEAH1. Overexpression of NtDEAH1 in both NC82 and JCP2 backgrounds significantly reduced LN, whereas CRISPR/Cas9-mediated knockout increased LN, indicating that NtDEAH1 acts as a negative regulator of LN and is a previously unreported control factor. Transcriptomic profiling and phytohormone analyses revealed that NtDEAH1 modulates the expression of genes in the gibberellin pathway. Specifically, NtDEAH1 binds to the 5'-untranslated region of the gibberellin receptor gene NtGID1, thereby influencing mRNA stability and translational efficiency to regulate LN. These findings provide new insights into genetic and molecular mechanisms underlying LN determination, and suggest that NtDEAH1 may serve as a target for future breeding aimed at optimising plant architecture and enhancing yield.