Brachypodium distachyon As a Model System For Understanding Iron Homeostasis In Grasses

While non-grass species use a combination of soil acidification and iron reduction to obtain sparingly soluble iron from the soil, grasses synthesize and secrete Fe(III) chelating agents called phytosiderophores (PS). When chelated by PS, Fe(III) solubility in the rhizosphere increases and Fe(III)-PS complexes are taken up into the root via specific transporters of the Yellow Stripe1 family at the plasma membrane. How PS are released from the root cells after synthesis remains unknown.  We have investigated PS secretion in the model grass, Brachypodium distachyon (brachypodium), and find that 3-hydroxy-2'-deoxymugineic acid (HDMA) is the dominant type of PS secreted by brachypodium, and that secretion of HDMA is diurnally regulated. In our EMS-mutagenized brachypodium population, we identified a mutant line with leaf interveinal chlorosis, which we named interveinal yellow1 (ivy1). Foliar Fe application rescued the chlorotic phenotype. Metal content analyses revealed that mutant plants are low in Fe, Zn and Cu. HPLC analyses of PS in the roots and root exudates show that mutant plants are capable of synthesizing PS in normal amounts, but they do not release the PS from roots into the rhizosphere.  We will present our progress toward cloning the ivy1 gene, which is likely to reveal novel aspects of the PS secretion mechanism.