Similarities and Differences in the Acquisition of Fe and P by Dicot Plants

Abstract

This review deals with two essential plant mineral nutrients, iron (Fe) and phosphorus (P); the acquisition of both has important environmental and economic implications. Both elements are abundant in soils but are scarcely available to plants. To prevent deficiency, dicot plants develop physiological and morphological responses in their roots to specifically acquire Fe or P. Hormones and signalling substances, like ethylene, auxin and nitric oxide (NO), are involved in the activation of nutrient-deficiency responses. The existence of common inducers suggests that they must act in conjunction with nutrient-specific signals in order to develop nutrient-specific deficiency responses. There is evidence suggesting that P-or Fe-related phloem signals could interact with ethylene and NO to confer specificity to the responses to Fe-or P-deficiency, avoiding their induction when ethylene and NO increase due to other nutrient deficiency or stress. The mechanisms responsible for such interaction are not clearly determined, and thus, the regulatory networks that allow or prevent cross talk between P and Fe deficiency responses remain obscure. Here, fragmented information is drawn together to provide a clearer overview of the mechanisms and molecular players involved in the regulation of the responses to Fe or P deficiency and their interactions.

Ethylene and Phloem Signals Are Involved in the Regulation of Responses to Fe and P Deficiencies in Roots of Strategy I Plants

“…The existence of cross talk between the responses to Fe and P deficiency could be associated with common signals in the activation of both nutrient deficiency responses, such as ethylene (Nagarajan and Smith, 2012; García et al, 2015; Lucena et al, 2015; Song and Liu, 2015; Neumann, 2016; Lucena et al, 2018), nitric oxide (NO; Graziano and Lamattina, 2007; Meng et al, 2012) and auxin (Chen et al, 2010; Miura et al, 2011; Bhosale et al, 2018). In relation to ethylene, the results presented in Figure 3 show that opt3-2 and pho2 , which exhibit constitutive Fe or P responses, respectively, have greater ACC content in roots than Col-0.…”

“…As a result, plants enhance acquisition of Fe and P through morphological and physiological responses in their roots. Deficiency of either nutrient initiates similar root responses, such as development of subapical root hairs or cluster roots and the acidification of the rhizosphere or the production of organic acids (Lucena et al, 2015; Song and Liu, 2015; Neumann, 2016; Stetter et al, 2017; Bhosale et al, 2018; Lucena et al, 2018). A defining feature of Strategy I plants is the need to reduce Fe(III), the most abundant form of Fe in soils, to Fe(II), prior to acquisition.…”

“…In previous works, it has been found that P deficiency induces the expression of Fe-related genes; that Fe deficiency induces the expression of P-related genes and that both deficiencies induce the expression of ethylene-related genes (reviewed in García et al, 2015; Lucena et al, 2015; Lucena et al, 2018). Taken together, these results suggest the existence of cross talk between Fe and P deficiency.…”

“…Taken together, these results suggest the existence of cross talk between Fe and P deficiency. The upregulation of Fe acquisition genes under P deficiency is generally associated to the increased accumulation of Fe in leaves (Wang Y. H. et al, 2002; Misson et al, 2005; Hirsch et al, 2006; Ward et al, 2008; Zheng et al, 2009; Abel, 2011; Perea-García et al, 2013; Wang et al, 2014, Lucena et al, 2018). On the other hand, P fertilization excess causes Fe chlorosis in calcareous soils (Romera et al, 1992; Sánchez-Rodriguez et al, 2013; Henry et al, 2017) and Fe deficiency affects P content in leaves (de Kock, 1955).…”

“…Either work in the nineties revealed links between ethylene and responses to deficiencies of Fe (Romera and Alcántara, 1994) and P (Borch et al, 1999). Although the regulation of the genes related to these responses is not totally understood, ethylene has since been implicated in the activation of both Fe-related genes ( AtFIT , AtFRO2 , and AtIRT1 ; Lucena et al, 2006; Lucena et al, 2015; Lucena et al, 2018; García et al, 2011; García et al, 2015) and P-related genes ( AtPht1;4 and AtPAP17 ; Lei et al, 2011; Roldán et al, 2013). In all cases, the activating effect of ethylene was dependent on the Fe or P status of the plants (García et al, 2011; Lei et al, 2011; Neumann, 2016; Liu et al, 2017), which suggests the involvement of signals other than ethylene in gene activation (García et al, 2013).…”