Abstract

BackgroundUnder iron-deficient conditions, Chlamydomonas exhibits high affinity for iron absorption. Nevertheless, the response, transmission, and regulation of downstream gene expression in algae cells have not to be investigated. Considering that the MAPK pathway is essential for abiotic stress responses, we determined whether this pathway is involved in iron deficiency signal transduction in Chlamydomonas.ResultsArabidopsis MAPK gene sequences were used as entry data to search for homologous genes in Chlamydomonas reinhardtii genome database to investigate the functions of mitogen-activated protein kinase (MAPK) gene family in C. reinhardtii under iron-free conditions. Results revealed 16 C. reinhardtii MAPK genes labeled CrMAPK2–CrMAPK17 with TXY conserved domains and low homology to MAPK in yeast, Arabidopsis, and humans. The expression levels of these genes were then analyzed through qRT-PCR and exposure to high salt (150 mM NaCl), low nitrogen, or iron-free conditions. The expression levels of these genes were also subjected to adverse stress conditions. The mRNA levels of CrMAPK2, CrMAPK3, CrMAPK4, CrMAPK5, CrMAPK6, CrMAPK8, CrMAPK9, and CrMAPK11 were remarkably upregulated under iron-deficient stress. The increase in CrMAPK3 expression was 43-fold greater than that in the control. An RNA interference vector was constructed and transformed into C. reinhardtii 2A38, an algal strain with an exogenous FOX1:ARS chimeric gene, to silence CrMAPK3. After this gene was silenced, the mRNA levels and ARS activities of FOX1:ARS chimeric gene and endogenous CrFOX1 were decreased. The mRNA levels of iron-responsive genes, such as CrNRAMP2, CrATX1, CrFTR1, and CrFEA1, were also remarkably reduced.ConclusionCrMAPK3 regulates the expression of iron-deficiency-responsive genes in C. reinhardtii.

Highlights

  • Under iron-deficient conditions, Chlamydomonas exhibits high affinity for iron absorption

  • Bioinformatics Analysis of mitogen-activated protein kinase (MAPK) Genes in Chlamydomonas Sixteen homologous genes (Table 1), which are localized in chromosomes 1, 2, 3, 8, 12, 13, 16, and 17, were identified by searching the Chlamydomonas genome database with Blast

  • Fourteen of the MAPKs located in the cytosome were predicted by Euk-mPLoc2.0 except CrMAPK6 and CrMAPK14, which exist in the nucleus

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Summary

Introduction

Under iron-deficient conditions, Chlamydomonas exhibits high affinity for iron absorption. The response, transmission, and regulation of downstream gene expression in algae cells have not to be investigated. Considering that the MAPK pathway is essential for abiotic stress responses, we determined whether this pathway is involved in iron deficiency signal transduction in Chlamydomonas. Chlamydomonas reinhardtii (Volvocales, Chlorophyta) is a single-celled eukaryotic and flagellated green alga, whose three genetic systems located in the nucleus, chloroplast, and mitochondria can be used for transformation. This alga is regarded as a “photosynthetic yeast” because of its easy culturing process, rapid growth, short life cycle, and high photosynthetic efficiency.

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