Genome-wide Survey of bHLH Super Gene Family in Brassica napus and Their Roles in Roots
Abstract Background: Basic helix-loop-helix (bHLH) gene family is one of the largest transcription factors in plants and are functionally characterized in diverse species. However, less is known about their functions in the economically important allopolyploid oil crop, Brassica napus . Results : We identified 602 potential bHLHs in B. napus genome ( BnbHLHs ) and categorized them into 36 subfamilies, including seven newly separated subfamilies, based on phylogeny, protein structure and exon-intron organization analysis. The intron insertion patterns of this gene family were corrected and a total of eight types were identified in the bHLH regions of BnbHLHs . Chromosome distribution and synteny analyses revealed that hybridization between Brassica rapa and Brassica oleracea was the main expansion mechanism for BnbHLHs . Expression analyses showed that BnbHLHs were wide and formed six main patterns, suggesting they may participate in various aspects in B. napus during the development. The expression profiles under five hormone treatments (IAA, ABA, ACC, GA3, 6-BA) in roots further revealed the active response of BnbHLHs with a large proportion of which being induced. qRT-PCR analysis confirmed the expression profiles of five candidate BnbHLHs under five hormone inductions. Up to 246 BnbHLHs from nine subfamilies were predicted to have potential roles relating to root development by joint analysis of expression profile and homolog function. Further, the MYB/bHLH/WD40 (MBW) protein complex regulating root hair development were verified in B. napus by yeast two-hybrid experiment. Conclusion: The 602 BnbHLHs identified from B. napus could be classed into 36 subfamilies, and those members from the same subfamily generally have similar sequence motifs. BnbHLHs may widely involve in root biological process in B. napus . Overall, this study provides important insights into the characterization and potential functions of B. napus bHLH super gene family and thus will be useful in future gene function research.