Expression Pattern and Functional Analysis of MebHLH149 Gene in Response to Cassava Bacterial Blight

The significant reduction in cassava (<i>Manihot esculenta</i> Crantz) yields attributed to cassava bacterial blight (CBB) constitutes an urgent matter demanding prompt attention. The current study centered on the MebHLH149 transcription factor, which is acknowledged to be reactive to CBB and exhibits augmented expression levels, as indicated by laboratory transcriptome data. Our exploration, encompassing <i>Xanthomonas phaseoli</i> pv. <i>manihotis</i> strain CHN01 (<i>Xpm</i> CHN01) and hormone stress, disclosed that the <i>MebHLH149</i> gene interacts with the pathogen at the early stage of infection. Furthermore, the <i>MebHLH149</i> gene has been discovered to be responsive to the plant hormones abscisic acid (ABA), methyl jasmonate (MeJA), and salicylic acid (SA), intimating a potential role in the signaling pathways mediated by these hormones. An analysis of the protein's subcellular localization suggested that MebHLH149 is predominantly located within the nucleus. Through virus-induced gene silencing (VIGS) in cassava, we discovered that <i>MebHLH149</i>-silenced plants manifested higher disease susceptibility, less ROS accumulation, and significantly larger leaf spot areas compared to control plants. The proteins MePRE5 and MePRE6, which are predicted to interact with MebHLH149, demonstrated complementary downregulation and upregulation patterns in response to silencing and overexpression of the <i>MebHLH149</i> gene. This implies a potential interaction between MebHLH149 and these proteins. Both <i>MePRE5</i> and <i>MePRE6</i> genes are involved in the initial immune response to CBB. Notably, MebHLH149 was identified as a protein that physically interacts with MePRE5 and MePRE6. Based on these findings, it is hypothesized that the <i>MebHLH149</i> gene likely functions as a positive regulator in the defense mechanisms of cassava against CBB.