The Structure, Evolution, and Expression Patterns Analysis Reveals the bHLH Members Associated with Powdery Mildew Resistance in Rubber Tree

The basic helix-loop-helix (bHLH) transcription factors play a crucial role in plant development and stress resistance. Elucidating the structure and function of bHLH family members related to rubber tree powdery mildew (<i>Erysiphe quercicola</i>) is essential for breeding disease-resistant rubber tree varieties. In the rubber tree (<i>Hevea brasiliensis</i> Muell. Arg.) variety CATAS73397, 204 HbbHLH transcription factors were systematically identified at the genome level and classified into 15 subfamilies through evolutionary analysis. The expansion of this family was primarily driven by whole-genome duplication (WGD). Based on RNA-seq data from leaves infected with powdery mildew, 11 <i>HbbHLH</i> genes responsive to infection were identified. Phylogenetic analysis examined the evolutionary relationships between rubber tree <i>bHLH</i> genes and disease-resistant <i>bHLH</i> genes from other plants. Promoter analysis of the 11 differentially expressed genes revealed abundant cis-elements associated with light responses, hormones, and transcription factor binding. Quantitative Real-time polymerase chain reaction validation indicated that <i>HbbHLH87</i> and <i>HbbHLH162-2</i> were significantly downregulated during infection, whereas <i>HbbHLH25</i> was significantly upregulated. These three genes exhibited strong responses to methyl jasmonate (MeJA) and salicylic acid (SA) treatments, suggesting their involvement in jasmonic acid and SA signal transduction pathways during the immune response. This study provides important insights into the molecular mechanisms underlying disease resistance in rubber trees and identifies potential targets for breeding disease-resistant varieties.