Iron deficiency-mediated stress regulation of four subgroup Ib BHLH genes in Arabidopsis thaliana

Abstract

Networks of transcription factors control physiological, developmental and environmental responses. Root iron acquisition responses are controlled by the essential bHLH protein FIT. Recently, two group Ib BHLH genes were reported to be iron deWciency-regulated. Here, we studied expression patterns of these two group Ib BHLH genes and of their two closest homologs to analyze whether their regulation would support a function in iron deWciency responses. We found that BHLH038, BHLH039, BHLH100 and BHLH101 (comprising a subgroup of BHLH Ib genes) were up regulated by iron deWciency in roots and leaves. Single insertion mutants had no visible phenotype and were capable of inducing root iron acquisition responses, presumably due to functional redundancy. SpeciWc metal treatments like nickel, high zinc or high copper resulted in induction of the four BHLH Ib genes whereas high iron, low copper and low zinc repressed gene expression. Induction of the four BHLH Ib genes was also found in multiple iron acquisition mutants including Wt. Ectopic activation of FIT did not suppress the four BHLH Ib genes. Split-root analyses using promoter-GUS lines showed that FIT and BHLH100 promoters were controlled by diVerent local and systemic signals involved in their regulation by iron. These results indicated that the four BHLH Ib genes were induced independently from FIT by conditions causing iron deWciency. Taken together, BHLH038, BHLH039, BHLH100 and BHLH101 function diVerently from FIT and may be involved in mediating a signal related to iron deWciencyinduced stress and/or internal iron homeostasis.

Improved iron acquisition ofAstragalus sinicusunder low iron-availability conditions by soil-borne bacteriaBurkholderia cepacia

“…In fact, plants have developed complex regulatory mechanisms to adapt to Fe deficiency (Jin et al 2007;Kim and Guerinot 2007;Rodrí-guez-Celma et al 2011). Some genes involved in the plant's Fe acquisition play crucial roles in the regulation of Fe accumulation in plants (Wang et al 2007;Yuan et al 2008). Here, the inoculation with JFW16 alleviated chlorotic symptoms in plants with the enhanced Fe assimilation under alkaline stress, suggesting that B. cepacia JFW16 provoked Fe deficiency responses effectively.…”

“…Strategy I plants including nongraminaceous monocots and dicots primarily rely on the reduction-based Fe acquisition mechanism by three processes: (I) root release of protons into rhizosperic soils for augmenting the solubility of Fe 3+ oxyhydroxides, and this process is dependent on the activity of plasma membrane H + -ATPase (AHA2) (Santi and Schmidt 2009); (II) the conversion of Fe 3+ to Fe 2+ by the ferric-chelate reductase (FCR) (FRO2) (Connolly et al 2003); and (III) the transportation of Fe 2+ into the epidemic cells of roots via the plasma-localized iron-regulated transport (IRT1) protein (Vert et al 2002). Moreover, these individual components of Fe acquisition machines in plants are finely controlled by Fe deficiencyinduced transcription factors (FIT) such as FIT1, bHLH38 and bHLH39 (Wang et al 2007;Yuan et al 2008). However, plants equipped with the Fe reduction-based mechanism often display typical symptoms of Fe deficiency under alkaline conditions (Xiong et al 2013;Zhou et al 2016).…”

Arabidopsis thaliana transcription factors bZIP19 and bZIP23 regulate the adaptation to zinc deficiency

“…The identification of these transcription factors, as well as the ZDRE cis element they bind to and the target genes they regulate, constitutes an important step forward toward unraveling the regulation of the zinc homeostasis network in plants. Up to now, the best studied plant micronutrient homeostasis regulatory network is the iron deficiency response involving bHLH transcription factors such as the Arabidopsis FIT, bHLH038, bHLH039, bHLH100, and bHLH101 genes (22)(23)(24), for which no transcription factor binding site has been found yet, and the rice IDEF1 and IDEF2 proteinsbelonging to the ABI3/VP1 and NAC families of transcription factors-binding respectively to the IDE1 and IDE2 iron-deficiencyresponsive elements (25,26). The Arabidopsis bHLH transcription factors are strongly affected by iron status of the plant, whereas the rice transcription factors are not iron-regulated, more resembling the poor induction of bZIP19 and bZIP23 gene expression by zinc deficiency.…”

Nicotianamine Functions in the Phloem-Based Transport of Iron to Sink Organs, in Pollen Development and Pollen Tube Growth in Arabidopsis

“…Gene expression analysis was performed by quantitative real-time RT-PCR as previously described (Wang et al, 2007;). Briefly, DNase-treated RNA was used for cDNA synthesis.…”