Gene Regulation of Iron-Deficiency Responses Is Associated with Carbon Monoxide and Heme Oxydase 1 in Chlamydomonas reinhardtii

Zhang Liping,Liu Zhaopu,Shao Hongbo,Long Xiaohua

doi:10.1371/journal.pone.0053835

Abstract

Carbon monoxide (CO) as an endogenous gaseous molecule regulates a variety of biological processes in animals. However, CO regulating nutrient stress responses in green alga is largely unknown. On the other hand, heme oxydase (HO1 as a rate-limiting enzyme of the first step for heme degration and to catalyze heme into biliverdin (BV), which is concomitant with releasing of CO and ferrous ions, probably participates in the process of CO-regulating response to nutrient stress in green alga. In this paper, we described an observation that CO could regulate iron-homeostasis in iron-starving Chlamydomonas reinhardtii. Exogenous CO at 8 µM was able to prevent the iron deficient-inducing chlorosis and improve chlorophyll accumulation. Expression pattern of FOX1, FTR1 and ferredoxin was up-regulated by CO exposure in iron-deficient mediam. treatment with external CO increasing iron accumulation in iron-deficient C. reinhardtii. Moreover, to get insights into the regulatory role of HO1, we constructed a transgenic alga overexpressing HO1 and HO1 knock-out mutants. The results show that there was no significant influence on chlorosis with HO1 overexpression of C. reinhardtii under iron-deficiency and the chlorophyll accumulation, and gene expression associated with iron deficiency of mutant were greatly improved. Otherwise, those results from HO1 knock-out mutants were opposite to HO1 overexpression mutants. Finally, CO exposure induced NO accumulation in cells. However, such an action could be blocked by NO scavenger cPTIO. These results indicate that CO/HO1 may play an important role in improving green algae adaptation to iron deficiency or cross-talking with NO under the iron deficiency.

Highlights

Iron (Fe) as an essential element is required for various cellular and physiological processes from respiration to photosynthesis
carbon monoxide (CO)/HO1 prevents chlorosis in iron-deficient algae Just because chlorosis is a remarkable symptom of iron deficiency, firstly, we tested whether exogenous CO could improve cell greening in iron-deficient algae
We found that heme oxygenase (HO)/OX completely performed green under iron deficiency, while HO/KO showed more serious chlorosis compared to wild-type (Figure 1b)

Summary

Introduction

Iron (Fe) as an essential element is required for various cellular and physiological processes from respiration to photosynthesis. Abundant iron is often unavailable for crops due to its low solubility of oxidized form (Fe3+) in farmland. Anaerobic conditions in acidic soils may lead to cellular iron overload, triggering toxicity to plants [1]. The iron levels in plant cells must be strictly regulated. Iron abundance in plants is primarily regulated by uptake, translocation and recycling. In Arabidopsis (strategy I plant species), iron uptake is controlled by at least three steps, including acidification of the rhizosphere by an H+-AT-Pase, reduction of Fe (III) to Fe (II) by ferric chelate reductases, and uptake of Fe (II) by transporters, while in Chlamydomonas reinhardtii, mobilization of iron from extracellular domain to intracellular fraction is involved in reduction of Fe by ferrireductases at the cell surface, and transported by iron transporters, like FTR1 [2]

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