Role of Heme Oxygenase in LATD/NIP-regulated ROS homeostasis and during nodule senescence in Medicago truncatula
Parna studied botany and molecular genetics at the University of Calcutta where she earned her bachelors and masters respectively. She joined the CMB Program in the fall of 2009 and is interested in molecular genetics. Outside of earning her PhD, Parna enjoys reading, walking and cooking.
Heme Oxygenase (HO) is an enzyme universally found in animals, plants and microbes. In plants, the role of heme oxygenase in the synthesis of the phytochrome chromophore is well recognized and has been extensively studied; however its role in regulating reactive oxygen species (ROS) in plants is just beginning to be explored, particularly in legumes. Legumes interact with Rhizobium bacteria to form symbiotic nitrogen fixing nodules. ROS plays an important role in the development of roots as well as nodules.
In the model legume Medicago truncatula, extracellular ROS in the root is regulated by the LATD/NIP gene. The heme oxygenase gene in M. truncatula is called GIRAFFE, we have a mutation that deletes the entire coding sequence. I am currently testing the role of M. truncatula GIRAFFE HO in regulating expression of LATD/NIP-regulated ROS genes. I found that in roots, the wild-type function of GIRAFFE is to upregulate expression of RBOHA, that functions in the generation of superoxide (an ROS). The effect of GIRAFFE on RBOHA is opposite to the effect of LATD/NIP, which is required to downregulate RBOHA expression in roots. My results show that LATD/NIP does not regulate GIRAFFE expression. I am investigating the role of GIRAFFE in the regulation of other LATD/NIP-regulated ROS genes.
Gene expression studies have revealed that at the time of senescence of M. truncatula nodules (structures in legume roots that fix nitrogen), the expression of heme oxygenase is the highest amongst all kinds of tissue. I am looking into how the loss of GIRAFFE HO function can alter the process of nodule senescence, by looking at ROS accumulation and gene expression studies of ROS-related genes and senescent markers.
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