The outer membrane Omp85-like protein P39 influences metabolic homeostasis in mature Arabidopsis thaliana

2018 
Omp85 proteins form a large membrane protein family found in bacteria and eukaryotes. Omp85 proteins are composed of a C-terminal β-barrel-shaped membrane domain and one, or more, N-terminal polypeptide-transport-associated (POTRA) domain(s). However, Arabidopsis thaliana contains two genes coding for Omp85 proteins without POTRA domain. One gene is designated P39, according to the molecular weight of the encoded protein. The protein is targeted to plastids and it was established that p39 shows electrophysiological properties similar to the other Omp85 family members, particularly to the one designated Toc75V/Oep80. We analyzed the expression of the gene and characterized two T-DNA insertion mutants with focus on alterations in photosynthetic activity, plastid ultrastructure, global expression profile, and metabolome. We observed pronounced expression of P39 especially in veins. The mutants of P39 show growth aberrations, reduced photosynthetic activity and changes of the plastid ultrastructure particularly in the leaf tip. Further, they display global alteration of gene expression and metabolite content in leaves of mature plants. We conclude that the function of the plastid localized and vein specific Omp85 family protein p39 is important, but not essential for maintenance of the metabolic homeostasis of full-grown Arabidopsis thaliana plants. Further, the function of p39 in veins influences the functionality of other plant tissues. The link connecting p39 function with metabolic regulation in mature Arabidopsis thaliana is discussed.
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