Molecular Mechanism of NtHD9 in Promoting Head Development of Long Glandular Trichomes in Tobacco

To explore the regulatory network of NtHD9 involved in the formation of long glandular trichomes (LGTs), analyses were conducted on NtHD9-SM, NtHD9-DM, NtHD9-OE plants. The expression levels of genes involved in jasmonic acid (JA) synthesis, metabolism and signal transduction were examined in wild-type (WT) and NtHD9 transgenic plants. Results revealed that both the size of glandular heads in LGTs and JA content followed the same order across the four lines: NtHD9-OE>WT>NtHD9-SM>NtHD9-DM. With increasing concentrations of methyl jasmonate (MeJA), the densities and sizes of LGT glandular heads in NtHD9-SM and NtHD9-DM plants increased, with head morphology normalizing at 200 μmol/L MeJA. RT-qPCR analysis revealed that NtHD9 expression was positively correlated with JA synthesis-related gene (LOX1, AOS and AOC2), JA metabolic gene (JAR1), JA signal transduction gene CYP94C1, several NtJAZ family members (NtJAZ3, NtJAZ5 and NtJAZ7), and NtHD-ZIP Ⅳ family members (NtHD3, NtHD7, NtHD9, NtHD11 and NtHD12). These genes exhibited decreased expression in NtHD9-SM and NtHD9-DM plants, while increased expression in NtHD9-OE plants. Conversely, three JA signaling-related genes (WRKY62, WRKY68 and NtJAZ12) showed the opposite trend, showing increased expression in NtHD9-SM and NtHD9-DM plants, and decreased expression in NtHD9-OE plants. These results indicatethat NtHD9 positively regulates the formation of glandular head in LGTs through JA signaling pathway in tobacco.