An HD-Zip III transcription factor, BjPHVa, negatively regulates non-glandular trichome formation in Brassica juncea

Trichomes are specialized structures derived from epidermal cells. Non-glandular trichomes primarily protect plants from herbivores and intense ultraviolet radiation by acting as a physical barrier. Recent research has highlighted the importance of homeodomain leucine zipper (HD-Zip) IV transcription factors (TFs) in promoting trichome development. In this study, an HD-Zip III TF called PHAVOLUTA (BjPHVa) was identified as a negative regulator of non-glandular trichome initiation in Brassica juncea. Genome editing of BjPHVa resulted in a significant increase in trichome number in B. juncea. Co-expression networks revealed a strong association between trichome development and the HD-Zip family, which was supported by transcriptomic analysis findings. An R2R3-MYB TF, BjGL1a, a key regulator of trichome development, was found to be associated with BjPHVa-regulated trichome development. Knockdown of BjGL1a expression resulted in reduced trichome number in B. juncea. BjPHVa was observed to interact directly with BjGL1a while binding to the BjGL1a promoter, resulting in the inhibition of BjGL1a transcription. These results provide new insights into the identification of regulators involved in trichome development and offer new opportunities to enhance resistance to predicted stresses through genome editing targeting PHVa within Brassicaceae.