A part of the upstream promoter region of SHN2 gene directs trichome specific expression in Arabidopsis thaliana and heterologous plants

- Detailed characterization of a promoter trap mutant line trip reveals that a part of upstream sequences of the SHN2 gene (−594/−30) region is required for trichome specific gene expression in Arabidopsis.
- The identified promoter region effectively regulates trichome specific expression in the heterologous systems i.e. both in Brassica juncea and Solanum lycopersicon.
- This study reveals an added benefit of using T-DNA tagging in identifying promoter elements that are not obvious from the expression profile of the concerned native gene.

A promoter trap mutant line of Arabidopsis carrying a promoterless β-glucuronidase (uidA) gene exhibited GUS expression predominantly in all the trichomes. In this mutant, the T-DNA insertion was localized at 147 bp upstream of the putative start codon, ATG, of the At5g11190 (SHN2) gene. Transcript profiling of the SHN2 suggested a constitutive expression of the gene in all the tissues. Deletion analysis of the upstream sequences established that a 565 bp (−594/−30) region confers trichome-specific gene expression. The trichomes isolated from young, mature and senesced leaf tissues also showed the presence of SHN2 transcript. The occurrence of multiple TSSs on the SHN2 gene sequence, presence of the SHN2 transcript in the homozygous trip mutant, despite an insertional mutation event, and diverse reporter gene expression pattern driven by 5′ and 3′ promoter deletion fragments, suggest a complex transcriptional regulation of SHN2 gene in Arabidopsis. The promoter sequence −594/−30 showed a conserved functional role in conferring non-glandular trichome-specific expression in other heterologous systems like Brassica juncea and Solanum lycopersicon. Thus, in the present study T-DNA tagging has led to the identification of a trichome-specific regulatory sequence in the upstream region of a constitutively expressed SHN2 gene. The study also suggests a complex regulation of SHN2 gene. Isolated trichome specific region retains its functions in other systems like Brassica and tomato, hence could be effectively exploited in engineering trichome cells in heterologous crop plants to manipulate traits like biopharming and insect herbivory.