Characterization of the maize b-32 ribosome inactivating protein and its interaction with fungal pathogen development

Abstract

Plants respond to attack by pathogenic fungi with a complex network of responses, including the production and accumulation of proteins, such as the Ribosome Inactivating Proteins (RIPs) that are toxic or inhibitory to pathogens. In maize endosperm, a cytosolic albumin termed b-32 (RIP1) is synthesized in temporal and quantita¬tive coordination with the deposition of storage proteins. Research has shown that b-32 is able to i) enzymati¬cally inactive ribosomes modifying rRNA inhibiting protein synthesis in vitro, ii) inhibit the growth of Rhizoctonia solani mycelia in an in vitro and in planta assays, iii) reduce Fusarium culmorum head blight in wheat transgenic plants expressing b-32, and iv) diminish Fusarium verticillioides attack symptoms in leaf tissues assays of maize transgenic expressing ectopically b-32 protein. Similarly to other RIPs, maize b-32 is accumulated in the seed as an inactive precursor, which is converted into an active form by proteolytic processing which removes peptide segments from the N (residues 1-16 of pro-RIP) and C (residues 295-301) termini and also from the center (linker domain) of the polypeptide. In this review we will summarize evidence and advances related to the ability of the b-32 protein in contrasting pathogen attacks by considering and describing i) in vivo b-32 antifungal activity and ii) in vitro fungal development inhibition. These data provide information for assessing b-32 in developing plants with a higher capacity to contrast damages induced by pathogens.