Publications - Faculty - Recently Submitted Faculty Publications 2008
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Burns - Plant Physiology
Regulation of Phospholipase Ds by Light and Ethylene Alters Sensitivity to Ethylene-Induced Leaf Abscission in Citrus
Anish Malladi and Jacqueline K. Burns
Abstract. Understanding leaf and fruit abscission is essential to develop strategies for regulation and control of abscission in fruit crops such as citrus. Several factors such as ethylene and light are known to regulate abscission signaling. In this study, we investigated molecular mechanisms involved in signaling Citrus sinensis cv. ‘Valencia’ leaf abscission. The ethylene-releasing compound ethephon induced rapid and extensive leaf abscission in citrus. A temperature-independent diurnal fluctuation in sensitivity to ethephon-induced leaf abscission was observed, with peak sensitivity during mid-day. Exposure to light was essential to facilitate ethylene-induced abscission of whole-leaf explants. At least 6 h of light exposure was required to facilitate this response. Previous studies suggested a role for phospholipid signaling in citrus abscission; hence, two phospholipase D cDNA sequences, CsPLDα1 and CsPLDγ1, were isolated from citrus and their role in ethylene-mediated abscission was examined. CsPLDα1 and CsPLDγ1 exhibited strong diurnal rhythms in expression with peak transcript accumulated around mid-day, coinciding with increased sensitivity to ethephon-induced abscission. While diurnal fluctuation in CsPLDα1 expression appeared to be entrained by light, CsPLDγ1 expression was regulated both by light and the circadian clock mechanism. In addition, CsPLDγ1 expression in leaves was up-regulated 3-fold after 3 h of ethephon treatment. We propose that PLDs mediate light and ethylene effects on abscission sensitivity.
