Iron (Fe) is indispensable for plant growth and development. It is crucial to maintain Fe homeostasis in plants. Previous studies have described the systems responsible for reduction, uptake and translocation of Fe. However, the molecular mechanism by which plants sense Fe status and coordinate the expression of Fe deficiency responsive genes is largely unknown.

Prof. YU Diqiu and his team of Xishuangbanna Tropical Botanical garden (XTBG) identified two basic helix-loop-helix-type transcription factors, bHLH34 and bHLH104 in Arabidopsis thaliana, by screening regulators upstream of bHLH101. Mutational analysis suggested that HLH34 and bHLH104 positively regulated Fe deficiency response. The researchers characterized that both bHLH34 and bHLH104 activated the transcription of bHLH38/39/100/101 and they non-redundantly regulated Fe deficiency responses in Arabidopsis thaliana.

They found that both bHLH34 and bHLH104 regulated bHLH101 gene. Neither bHLH34 nor bHLH104 was affected by Fe deficiency. They also observed that the amiR-bhlh34/104 plants phenocopied the bhlh34bhlh104 mutants. bHLH34 and bHLH104 were required for maintaining Fe homeostasis in both Fe-sufficient and -deficient conditions. bHLH34 and bHLH104 acted upstream of bHLH38/39/100/101 and FE-DEFICIENCY INDUCED TRANSCRIPTION FACTOR (FIT). HLH34 and bHLH104 positively regulated Fe deficiency response. Overexpression of bHLH34 and bHLH104 activated Fe deficiency response. bHLH34 and bHLH104 directly regulated transcription of bHLH38/39/100/101. Overexpression of bHLH101 partially rescued bhlh34bhlh104 mutants. bHLH34 could physically interact with bHLH104.

The research results revealed that bHLH34 and bHLH104 played major roles in regulating Fe homeostasis by activating the transcription of bHLH38/39/100/101 under Fe deficiency conditions.

The study was supported by the Youth Innovation Promotion Association of CAS, Candidates of the Young and Middle Aged Academic Leaders ofYunnan Province and the program for Innovative Research Team of Yunnan Province.

The study entitled “Two bHLH Transcription Factors, bHLH34 and bHLH104, Regulate Iron Homeostasis in Arabidopsis thaliana” has been published online in Plant Physiology.