Ethylene Participates in the Regulation of Fe Deficiency Responses in Strategy I Plants and in Rice

Abstract

Iron (Fe) is very abundant in most soils but its availability for plants is low, especially in calcareous soils. Depending on the strategies developed to acquire it, plants have been divided into Strategy I and Strategy II plants. Strategy I plants apply a reduction-based strategy and include all higher plants except the Gramineae, while Strategy II plants apply a chelation-based strategy and include the Gramineae. To cope with Fe deficiency both type of plants activate several Fe deficiency responses, mainly in their roots. These responses need to be tightly regulated to avoid Fe toxicity and to conserve energy. Their regulation is not totally understood but some hormones and signaling substances have been implicated, mainly in Strategy I plants. In these plants, several years ago it was suggested the participation of ethylene in the regulation of Fe deficiency responses. In Strategy II plants, the role of hormones and signaling substances have been less studied. However, in rice, a Strategy II plant that possesses some characteristics of Strategy I plants, it has been recently shown that ethylene can also play a role in the regulation of some of its Fe deficiency responses. In this review, we will review and discuss the data supporting a role for ethylene in the regulation of responses to Fe deficiency in both Strategy I and Strategy II plants. In addition, we will discuss the results suggesting the action of ethylene through different transduction pathways and its interaction with other signals, such as some probable Fe-related repressive signals moving through the phloem.