Interplay Between Silicon and Iron Signaling Pathways to Regulate Silicon Transporter Lsi1 Expression in Rice

Abstract

Silicon (Si) is not an essential element, but it is a beneficial element for growth and development of many plant species. Nevertheless, how plants regulate the initial uptake of silicon (Si) remains poorly understood. It has been proposed that the regulation of Si uptake is largely regulated by Si availability. However, the current model is clearly reductionist and does not consider the availability of essential micro-elements such as iron (Fe). Therefore, the present study investigates the regulation of the Si transporter Lsi1, in three rice varieties grown under different Si and Fe regimes. The Lsi1 transcript was compared to intracellular concentrations of Si and Fe in roots. The amount of Lsi1 transcript was mainly altered in response to Si-related treatments. Split-root experiments showed that the expression of Lsi1 is locally and systemically regulated in response to Si signals. Interestingly, the accumulation of Lsi1 transcripts appeared to be dependent on Fe availability in root growth environment. Results suggest that the expression of Lsi1 depends on a regulatory network that integrates Si and Fe signals. This response was conserved in the three rice cultivars tested. This finding is the first step toward a better understanding of the co-regulation of Si homeostasis with other essential nutrients in plants. Finally, our data clearly show that a better understanding of Si/Fe signaling is needed to define the fundamental principles supporting plant health and nutrition.

Interactions of Silicon With Essential and Beneficial Elements in Plants

“…Exudation of organic ligands (mainly PSs) by roots of Fe deficient barley plants can indirectly increase Si availability in the rhizosphere ( Gattullo et al, 2016 ), as a consequence of nutrient (e.g., Fe) mobilization from silicate minerals by liberation of silicic acid. In rice roots, low supply of both N and Fe led to up-regulation of OsLsi1 ( Wu et al, 2017 ; Chaiwong et al, 2020 ) and OsLsi2 ( Wu et al, 2017 ). A similar effect was observed in K-deficient barley, where up-regulation of HvLsi1 , HvLsi2 and HvLsi6 was responsible for accumulation of Si in the shoot ( Hosseini et al, 2017 ).…”

“…Increasing evidence suggests that nutritional status can affect Si accumulation and distribution in plants (e.g., Kim et al, 2014 ; Bokor et al, 2015 ; Hosseini et al, 2017 ; Wu et al, 2017 ; Chaiwong et al, 2020 ; Minden et al, 2020 ; Xiao et al, 2021 ). However, only a few studies have investigated the effect of specific nutrient imbalances on the expression of Si transporters and could be additionally affected by the Si concentration in the shoot ( Mitani-Ueno and Ma, 2020 ).…”

“…However, only a few studies have investigated the effect of specific nutrient imbalances on the expression of Si transporters and could be additionally affected by the Si concentration in the shoot ( Mitani-Ueno and Ma, 2020 ). It has been shown that limited supply of the macronutrients (N, P, K) and the micronutrient Fe, can induce Si accumulation in plant roots and/or shoots ( Wu et al, 2017 ; Chaiwong et al, 2018 , 2020 ; de Tombeur et al, 2020 ; Minden et al, 2020 ). Exudation of organic ligands (mainly PSs) by roots of Fe deficient barley plants can indirectly increase Si availability in the rhizosphere ( Gattullo et al, 2016 ), as a consequence of nutrient (e.g., Fe) mobilization from silicate minerals by liberation of silicic acid.…”

Silicon in the Soil–Plant Continuum: Intricate Feedback Mechanisms within Ecosystems

“…Expression of the Lsi1 gene in rice is downregulated by Si supply, dehydration stress and abscisic acid (more strongly in Si-depleted plants), suggesting regulation of active Si uptake in response to changes in the transpiration stream and plant internal water balance [ 123 ]. Further studies have demonstrated how the expression of Lsi1 , Lsi2 and Lsi6 genes is regulated by plant hormones [ 124 ] and internal Si and metal concentrations [ 125 , 126 ].…”

Interaction Between Macro‐ and Micro-Nutrients in Plants

“…A wealth of information has been generated during the last two decades on morphological and physiological adaptations of plants in response to the changes in the availability of mineral nutrients ( Gniazdowska and Rychter, 2000 ; Maathuis, 2009 ; Krouk et al, 2011 ; Gruber et al, 2013 ; Zhao and Wu, 2017 ; Krouk and Kiba, 2020 ). Protein-coding genes involved in the uptake, mobilization, storage, and assimilation of macro/micro-elements have been characterized to some extent; and regulatory networks affecting their expression in response to the changing nutritional status are being elucidated ( Schachtman and Shin, 2007 ; Giehl et al, 2009 ; Gojon et al, 2009 ; Liu et al, 2009 ; Pilon et al, 2009 ; Hindt and Guerinot, 2012 ; Vigani et al, 2013 ; Briat et al, 2015 ; Chaiwong et al, 2020 ). Crop plants are frequently subjected to nutrients imbalance which adversely affects several metabolic processes.…”