Unraveling dwarfing mechanisms in Hedychium: insights into HcNAC140 and HcEXPA4 functionality

The relatively tall stature of Hedychium limits its application in landscape gardening and pot cultivation while also posing challenges for crop management. Therefore, an in-depth understanding of the regulatory mechanisms controlling plant height is urgently needed to facilitate the development of suitable dwarf cultivars.  RESULTS: In this study, HcEXPA4, a gene that is significantly differentially expressed, was identified in the internode transcriptomes of Hedychium plants with extremely tall and dwarf phenotypes. Sequence alignment revealed that HcEXPA4 is functionally conserved with EXPA4 homologs from other species and is involved in regulating cell elongation. Virus-induced gene silencing (VIGS) of HcEXPA4 resulted in a dwarf phenotype in Hedychium seedlings. Conversely, the overexpression of HcEXPA4 significantly promoted plant height in tobacco. Through correlation analysis and RT‒qPCR, the upstream regulatory transcription factor HcNAC140 was further identified. Silencing HcNAC140 via VIGS notably reduced plant height in Hedychium seedlings and concurrently upregulated the expression of HcEXPA4. Moreover, the overexpression of HcNAC140 in tobacco led to a significant increase in plant height. The protein interaction assays further confirmed that HcNAC140 specifically binds to the CACG core motif within the HcEXPA4 promoter, directly activating its transcription.

This study elucidates the pivotal role of the HcNAC140-HcEXPA4 regulatory module in controlling plant height in Hedychium, providing a theoretical foundation and potential molecular targets for the architectural optimization and molecular breeding of this species.