Suppression of Shade- or Heat-induced Leaf Senescence in Creeping Bentgrass through Transformation with the ipt Gene for Cytokinin Synthesis

Abstract

<jats:p>Cytokinins have been associated with delaying or suppressing leaf senescence in plants. The objectives of this study were to determine whether the expression of the <jats:italic>ipt</jats:italic> gene that encodes adenine isopentenyltransferase would delay leaf senescence induced by shade or heat stress in a perennial grass species. Creeping bentgrass (<jats:italic>Agrostis stolonifera</jats:italic> cv. Penncross) was transformed with <jats:italic>ipt</jats:italic> isolated from agrobacterium (<jats:italic>Agrobacterium tumefaciens</jats:italic>) using two gene constructs (<jats:italic>SAG12-ipt</jats:italic> and <jats:italic>HSP18-ipt</jats:italic>) designed to activate cytokinin synthesis during shade or heat stress. Whole plants of nine <jats:italic>SAG12</jats:italic>-<jats:italic>ipt</jats:italic> transgenic lines and the nontransgenic control plants were incubated in darkness at 20 °C for 20 days. Chlorophyll content of all transgenic lines and the control line decreased after dark treatment, but the decline was less pronounced in transgenic lines. All transgenic lines had higher isopentenyladenine (iP/iPA) content than the control line after 20 days of treatment. In six of the transgenic lines, iP/iPA content remained the same or higher after dark treatment. Whole plants of nine <jats:italic>HSP18</jats:italic>-<jats:italic>ipt</jats:italic> transgenic lines and the control plants were incubated at 35 °C for 7 days. Chlorophyll and iP/iPA content declined in the control plants, but the nine transgenic lines had a significantly higher concentration of iP/iPA and were able to maintain chlorophyll content at the prestress level. Our results suggest that expression of <jats:italic>SAG12</jats:italic>-<jats:italic>ipt</jats:italic> or <jats:italic>HSP18</jats:italic>-<jats:italic>ipt</jats:italic> in creeping bentgrass resulted in increases in cytokinin production, which may have led to the delay and suppression of leaf senescence induced by shade or heat stress.</jats:p>

Genetic variation in yield under hot ambient temperatures spotlights a role for cytokinin in protection of developing floral primordia

“…Expressing the IPT gene involved in cytokinin biosynthesis, under the control of a senescence‐induced promoter (SAG) in transgenic creeping bentgrass, prevented a HAT‐induced reduction in cytokinin levels and significantly increased resistance to HAT (Xing et al . ; Xu et al . ; Xu, Gianfagna & Huang ; Merewitz et al .…”

“…Fourteen days of HAT (35°C) caused leaf senescence as well as a significant reduction in shoot iP and ZR levels in creeping bentgrass ). Expressing the IPT gene involved in cytokinin biosynthesis, under the control of a senescence-induced promoter (SAG) in transgenic creeping bentgrass, prevented a HAT-induced reduction in cytokinin levels and significantly increased resistance to HAT (Xing et al 2009;Xu et al 2009;Xu, Gianfagna & Huang 2010;Merewitz et al 2012). There are several other examples of SAG:IPT providing protection of seedlings against stress-or age-induced leaf senescence (Gan & Amasino 1995;Rivero et al 2007;Xu et al 2009).…”

The impact of heat stress targeting on the hormonal and transcriptomic response in Arabidopsis

“…Trans-zeatin riboside was also found to prevent decline of the activity of several antioxidant enzymes [10]. The ipt overexpression driven by SAG12 promoter prevented chlorophyll loss during HS [11]. Enhanced CK production driven by heat-inducible promoter was found to induce small heat shock protein and glycine-rich protein [9].…”

“…Apart from their effect on stomatal aperture, CKs were found to induce a small heat shock protein and a glycine-rich protein during HS [9]. Both exogenous application of CKs [10] and elevation of CK levels by overexpression of the biosynthetic gene isopentenyltransferase (ipt) under the senescence-inducible promoter (SAG12) resulted in elevation of HS tolerance [11]. Protective role of CKs on developing flowers exposed to HS was demonstrated [12].…”

Heat shock proteins: Changes related to aging, development of thrombotic complications, and peptide regulation of the genome

“…The interaction of HSPs with macrophageTLR2 and TLR4 was shown to induce an increase in the intracellular Ca 2+ concentration and the activation of the nuclear factor NFκB leading to increased produc tion of NO, IL 1b, IL 6, IL 12, IL 18, TNF α, chemokines and adhesion molecules promoting inflammatory reactions, endothelial damage and ath erosclerosis development [21,82]. An increase in the levels of IL 1, IL 12, IL 18, and IFNγ was shown to promote the progression of atherosclerosis in experi mental animals, while blocking the above named cytokines decreased the degree of atherosclerotic changes by 15-69% [51].…”