Functional characterization and comparative analysis of AtMYB42 and AtMYB85 promoters to gain insights into transcriptional regulation during development and hormonal induction

Abstract

The present study was designed to functionally characterize the promoters associated with AtMYB42, AtMYB85, and BjuMYB85. These genes are well known to be involved in lignin synthesis via phenylpropanoids, which are crucial for secondary cell wall development. We previously reported the complete absence of homologs of MYB42 from Brassica species. Inspite of their known role in secondary cell wall development, detailed knowledge about cis-element and transcriptional regulation of AtMYB42, AtMYB85 and BjMYB85 (BjuA013029) is lacking. It is therefore crucial investigating the transcriptional regulation of AtMYB42, AtMYB85, and BjMYB85 (BjuA013029), analyze functional and regulatory conservation and divergence and address whether BjMYB85 potentially compensates for the absence of MYB42 homologs in Brassica. In silico analysis revealed differences in the promoter sequences but shared transcription factor-binding sites and motifs, suggesting a common cis-regulatory pathway. Functional characterization using transcriptional fusion constructs revealed tissue-specific expression patterns not only in the stem, as has been reported earlier, but also in anther walls and siliques where lignin deposition plays an important role in dehiscence. Hormone and stress responsiveness of these promoters were assessed in seedlings. The AtMYB42 promoter displayed greater responsiveness to ethylene, cytokinin, and salicylic acid compared to AtMYB85 and BjuA013029MYB85. Expression was observed in various tissues, including seedlings, anthers, and silique and leaf midribs. This study provides novel insights into the expression patterns of these promoters, shedding light on their roles in non-stem tissues and contributing to our understanding of secondary cell wall formation.