| dc.description.abstract | Lipoxygenases (LOX) are enzymes that produce an array of oxylipins that regulate multiple plant physiological processes. ZmLOX10 is an important LOX isoform that is required for the synthesis of many diverse oxylipins, including its well-known and critical role in green leaf volatile (GLV) synthesis. Transgenic Arabidopsis over-expressing ZmLOX6 has also been implicated in synthesis of pentyl leaf volatiles (PLV). By utilizing genetic knockout mutants of Zea mays and transgenic over-expressors of Arabidopsis thaliana, I show that both ZmLOX6 and ZmLOX10 function in PLV synthesis in maize, and that PLV synthesis is partially dependent on jasmonic acid (JA) signaling. I also establish the biosynthetic order of analysis of PLVs through exogenous treatments with select PLVs, and that popular method of plant tissue volatile analysis, freeze-thawing, is flawed and provides erroneous results.
Compared to PLVs, significantly more is known regarding GLVs, including their well-known ability to induce synthesis of the important phytohormone, JA. JA is a key regulator of defense against both pathogens and insects. JA also shares strong antagonism with another phytohormone, salicylic acid (SA), that regulates defense against biotrophic and hemi-biotrophic pathogens. Studies detailing the impact of GLVs on plant-pathogen interactions have almost exclusively focused on necrotrophic pathogens, which showed that GLVs promote resistance. Utilizing GLV- and JA-deficient knockout mutants of maize and the hemi-biotrophic fungus, Colletotrichum graminicola, I show that GLVs induce susceptibility in maize to the anthracnose fungus, Colletotrichum graminicola. GLV-mediated susceptibility is accomplished by induction of JA, which in turn suppresses synthesis of SA.
In addition to being released in response to a wide variety of stresses, GLVs are also emitted in massive amounts after light-to-dark transitions. The physiological implications of this phenomenon had previously not been investigated. My results show that dark-induced GLV emission causes a brief spike in non-ZmLOX10-derived JA synthesis. I further show that these phenomena prime the plant for increased resistance to the insect herbivore, Spodoptera frugiperda (fall armyworm), and that this resistance lasts for at least 24 hours. Lastly, I show that GLVs are potent inducers of stomatal closure in maize, particularly GLV aldehydes. | en |
