EAGER-Forgotten N-conjugate cytokinins and their active role during senescence

Cytokinin is a plant hormone that is essential to normal growth and development in plants. One key function of cytokinin is to keep older leaves green and growing efficiently by delaying their eventual yellowing and aging, called senescence. Study of how cytokinin regulates the delay of senescence will help researchers learn how to increase growth, performance, and yield of agricultural crops.

Cytokinin is a blanket term for a class of about 30 chemically related compounds that regulate these growth processes. A sub-group of understudied cytokinin compounds, known as N-conjugate cytokinins, are also involved in delaying leaf senescence, yet their role and function are unknown. These N-conjugate cytokinins have not been examined for nearly 35-years and only recently were identified as being active regulators of this developmental process.

This research aims to understand the role of these forgotten cytokinins in leaf aging using classical bioassays and physiological measurement paired with cutting edge analyses. Graduate and undergraduate students will be trained in basic research, and summer research experiences will be offered to high school students to increase exposure to the plant sciences.

Nearly all cytokinin research has focused on cytokinin bases forms like trans-Zeatin (tZ) and isopentenyladenine (iP), which are known to bind cytokinin receptors and trigger canonical cytokinin responses, such as delaying senescence. Yet recently findings indicate that the unstudied N-conjugate cytokinins forms can also delay senescence suggesting a re-examination of the role of these N-conjugate during senescence.

Bioassays will be used to directly measure changes in the levels of all cytokinin forms and will use GC-MS/MS to determine effects on the cytokinin biosynthesis pathway during development. Transcriptome and proteome analyses during senescence will be conducted in parallel with physiology and measurements of cytokinin levels to characterize gene expression and protein changes that specifically occur in response to N-conjugate cytokinin vs base cytokinin forms.

This high risk and high reward endeavor should uncover the role of these otherwise under-studied cytokinins and explain how different cytokinin compounds delay senescence at the molecular level over development.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.