Heterologous expression of AcbHLH1 in tobacco affects trichome density and length

Background As the world’s largest producer and consumer of kiwifruit, China attaches significant socio-economic importance to this crop. Trichome initiation serves as a vital agronomic characteristic that provides protection against diverse biological and environmental challenges. Nonetheless, the specific functional genes governing this pathway in kiwifruit have not yet been fully elucidated. In this study, we characterized two kiwifruit lines with contrasting trichome densities: a low-density type of A. chinensis cv. HY-1 and a high-density type of A. eriantha cv. MH-1. Results A comparative analysis of the number and density of stem trichomes between the two kiwifruit hybrid lines was then performed. BSA analysis of leaves with high trichome dengsity and low trichome density pools from the F ₂ segregating population mapped the candidate genes on Chr.13. A candidate gene, AcbHLH1 , was subsequently cloned. Phylogenetic tree analysis revealed that the protein encoded by AcbHLH1 belongs to the atypical bHLH TF family. AcbHLH1 was found to localize in the nucleus. The tissue-specific expression profiles of AcbHLH1 were investigated quantitative real-time PCR (qRT-PCR). Transcript accumulation was markedly higher in mature organs (leaves, petioles, stems) and floral buds, whereas expression remained relatively low in young vegetative tissues. Overexpression of AcbHLH1 in Nicotiana tabacum caused a 37.03%–56.25% reduction in trichome density but a 70.24%–74.42% increase in trichome length on both leaves and stems. Conclusion Taken together, our results revealed that AcbHLH1 negatively regulates trichome density and positively regulates trichome length. This study elucidates a molecular mechanism underlying kiwifruit trichome development and provides a genetic target for breeding low-trichome kiwifruit cultivars.