In Chlamydomonas reinhardtii, the gene encoding Swiss:Q9LD42 is induced by iron deficiency [1]. In green algae, this protein is periplasmic. The two paralogues FEA1 and FEA2 are the major proteins secreted by iron-deficient Chlamydomonas reinhardtii, and both are up-regulated in response to iron deficiency. FEA1 but not FEA2 is up-regulated by high CO2 concentration. Both FEA1 and FEA2 are secreted into the periplasmic space and genetic evidence confirms that their association with the cell is required for growth in low iron [2].

1: Cadmium- and iron-stress-inducible gene expression in the green alga Chlamydomonas reinhardtii: evidence for H43 protein function in iron assimilation. Rubinelli P, Siripornadulsil S, Gao-Rubinelli F, Sayre RT; Planta 2002;215:1-13. PMID:12012236

2: FEA1, FEA2, and FRE1, encoding two homologous secreted proteins and a candidate ferrireductase, are expressed coordinately with FOX1 and FTR1 in iron-deficient Chlamydomonas reinhardtii. Allen MD, del Campo JA, Kropat J, Merchant SS; Eukaryot Cell. 2007;6:1841-1852. PMID:17660359