Pathogenesis related proteins in Dioscorea bulbifera L.: A study of the expression patterns of putative defense proteins in an invasive plant species

Plants experience a myriad of diverse stress stimuli which can be of either biotic or abiotic nature. Because they are sessile organisms they have had to evolve intricate defense mechanisms. Most are familiar with physical defense systems but less known and more complex are the chemical defenses. Chemical defenses include a special family of proteins called pathogenesis related (PR) proteins. These low molecular weight proteins can be constitutively expressed or highly inducible upon elicitation by fungal pathogens. The signaling pathways that lead to the expression of the PR proteins are regulated by the plant hormones salicylic acid (SA), jasmonic acid (JA), and abscisic acid (ABA). Western blot data provide evidence that the PR proteins chitinase and beta-1,3-glucanase are present in both leaf and tuber tissues of Dioscorea bulbifera L. Upon treatment of leaf tissue with SA, expression of a 47 kDa chitinase was up regulated after both 24 and 48 hours post treatment. Leaves treated with Fusarium graminearum cell wall fragments exhibited a unique triplet of bands with molecular weights of 28, 24, and 16 kDa. Tuber tissues exhibited constitutive expression of a 119 kDa and a 34 kDa chitinase and a 31 kDa beta-1,3-glucanase across all treatments including the controls. This thesis provides evidence that supports the role of chitinases and beta-1,3-glucanases as part of a defense response in aerial tubers and leaves of D. bulbifera L.