sentence: The above mentioned bHLHs display high degree of sequence similarity to four AtbHLH genes which encode AtbHLH038 ( ORG2 ) , AtbHLH039 ( ORG3 ) , AtbHLH100 and AtbHLH101 that functioned downstream of AtbHLH034-AtbHLH104-AtbHLH105 complex and separately interacted with FIT1 ( AtbHLH029 ) to constitutively regulate the expression of IRT1 ( high-affinity ferrous iron transporter ) and FRO2 ( ferric – chelate reductase ) [ 57 ] .