It limited conditions in Arabidopsis. FERULOYL-COA 6′-HYDROXYLASE 1

It is evident that nutrient uptake in plants needs tobe fine-tuned to counteract nutrient deficiency but also overaccumulation andhence toxicity. To date, two Fe uptake strategies have been investigated,concerning the uptake from the soil into epidermal cells. All plants except thePoaceae execute a Fe3+ reduction-baseduptake strategy (Strategy I). Poaceae,however, excrete non-proteinogenic amino acids, phytosiderophores, to complexFe3+ (Strategy II) (Marschner et al., 1986; Romheld and Marschner, 1986).  1.

1.1       Reduction-basedFe Uptake (Strategy I)The Fe uptake strategy employed by allnon-graminaceous plants, such as Arabidopsisthaliana, consists of three steps that are executed by Fe-responsive, plasma-membranelocalized proteins, located in epidermal root cells (Figure 1). Soil acidification allows solubilizing Fe3+which is bound to negatively charged soil particles (Step 1) (Marschner et al., 1986).

Best services for writing your paper according to Trustpilot

Premium Partner
From $18.00 per page
4,8 / 5
4,80
Writers Experience
4,80
Delivery
4,90
Support
4,70
Price
Recommended Service
From $13.90 per page
4,6 / 5
4,70
Writers Experience
4,70
Delivery
4,60
Support
4,60
Price
From $20.00 per page
4,5 / 5
4,80
Writers Experience
4,50
Delivery
4,40
Support
4,10
Price
* All Partners were chosen among 50+ writing services by our Customer Satisfaction Team

Several Arabidopsis ATPases wereshown to be responsive to Fe limitations, but one promising candidate was ArabidopsisH(+)-ATPASE2 (AHA2). aha2 knock-out mutants displayed asignificant reduction in net proton flux compared to WT when grown under sufficient and deficient Fe conditions, confirminga major role of AHA2 in rhizosphere acidification (Santi and Schmidt, 2009). Secretion of secondary metabolites can positivelyaffect the Fe uptake response. As seen in red clover, secreted phenoliccompounds enhance the utilization of apoplastic Fe3+ (Jin et al., 2007). Similarly, the expression ofrespective efflux transporter and the presence of phenolic compounds supportthe Fe uptake under limited conditions in Arabidopsis.

FERULOYL-COA 6′-HYDROXYLASE1 (F6’H1), a player in the phenylpropanoid biosynthesispathway, as well as the phenolic transporter PLEIOTROPIC DRUG RESISTANCE9 (PDR9) (also called ABCG37) are key players in Arabidopsis. Generally,the secretion of phenolic compounds and expression of ABCG37 are upregulated under Fe deficiency. Thus, it is believedthat the secretion of different phenolic compounds, such as coumarins, enhancesthe Fe3+ assimilation and mobilization. In Arabidopsis,especially the coumarin scopoletin seems to play an important role (Rodriguez-Celma etal., 2013; Fourcroy et al., 2014; Schmid et al., 2014; Schmidt et al.

, 2014;Fourcroy et al., 2016).Once Fe3+ is available, it is subsequentlyreduced to Fe2+ by FERRIC REDUCTASE-OXIDASE 2 (FRO2) (Robinson et al.

, 1999). FRO2 was identified based on itssequence similarity to yeast ferric-chelate reductases and the human phagocyticNADPH oxidase (Robinson et al., 1999). The respective loss-of-functionmutant frd1 shows decreased Fe chelatereductase activity (Yi and Guerinot, 1996).

When grown under Fe deficientconditions, the frd1 mutant phenotype,such as severe leaf chlorosis, could be complemented by FRO2 expression. Overexpression of FRO2 even enhanced tolerance to Fe deficiency (Robinson et al., 1999; Connolly et al., 2003) (Step2). In the last step, Fe2+is transported across the membrane from the rhizosphere into epidermal cells.

Ina yeast -complementation assay, IRON REGULATED TRANSPORTER1 (IRT1) was able torescue the growth defect of the Fe uptake mutant strain fet3/fet4 under limited Fe supply (Eide et al., 1996). irt1-1 knock-out mutants display severeFe deficiency chlorosis, growth defects, disturbed photosynthetic capacityunder Fe deficient conditions as well as reduced leaf Fe content when grown insoil. Hence, IRT1 is responsible for the Fe uptake in plants.  Interestingly, IRT1 is not highly selective,since it also transports other divalent metals in the plant (Henriques et al., 2002; Varotto et al., 2002; Vert etal.

, 2002). The question remained which upstream located regulatorcoordinates those processes and hence fine-tunes the action of the respective proteins,involved in Strategy I. The basic helix-loop-helix (bHLH) transcription factorFER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT, bHLH029), belongingto subgroup IIIa within the A. thaliana bHLH family (Heim et al.

, 2003), wasshown to execute this task. Upon dimerization with bHLH subgroup Ib proteins, bHLH038,bHLH039, bHLH100 and bHLH101, which are upregulated by Fe deficiencyindependently from FIT, FIT induces the expression of AHA2, FRO2 and IRT1 upon Fe limitation (Heim et al., 2003; Colangelo and Guerinot, 2004;Jakoby et al., 2004; Yuan et al., 2005; Vorwieger et al.

, 2007; Wang et al.,2007; Yuan et al., 2008; Ivanov et al., 2012; Wang et al., 2013; Mai et al.,2015; Mai et al., 2016; Naranjo-Arcos et al., 2017).

The question remained which upstream located regulatorcoordinates those processes and hence fine-tunes the action of the respective proteins,involved in Strategy I. The basic helix-loop-helix (bHLH) transcription factorFER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT, bHLH029), belongingto subgroup IIIa within the A. thaliana bHLH family (Heim et al., 2003), wasshown to execute this task. Upon dimerization with bHLH subgroup Ib proteins, bHLH038,bHLH039, bHLH100 and bHLH101, which are upregulated by Fe deficiencyindependently from FIT, FIT induces the expression of AHA2, FRO2 and IRT1 upon Fe limitation (Heim et al.

, 2003; Colangelo and Guerinot, 2004;Jakoby et al., 2004; Yuan et al., 2005; Vorwieger et al., 2007; Wang et al.

,2007; Yuan et al., 2008; Ivanov et al., 2012; Wang et al., 2013; Mai et al.,2015; Mai et al., 2016; Naranjo-Arcos et al.

, 2017).

x

Hi!
I'm Simon!

Would you like to get a custom essay? How about receiving a customized one?

Check it out