giganteaSuppressesimmutansVariegation by Interactions with Cytokinin and Gibberellin Signaling Pathways    

Abstract

The immutans (im) variegation mutant of Arabidopsis (Arabidopsis thaliana) is an ideal model to gain insight into factors that control chloroplast biogenesis. im defines the gene for PTOX, a plastoquinol terminal oxidase that participates in the control of thylakoid redox. Here, we report that the im defect can be suppressed during the late stages of plant development by gigantea (gi2), which defines the gene for GI, a central component of the circadian clock that plays a poorly understood role in diverse plant developmental processes. imgi2 mutants are late flowering and display other well-known phenotypes associated with gi2, such as starch accumulation and resistance to oxidative stress. We show that the restoration of chloroplast biogenesis in imgi2 is caused by a development-specific derepression of cytokinin signaling that involves cross talk with signaling pathways mediated by gibberellin (GA) and SPINDLY (SPY), a GA response inhibitor. Suppression of the plastid defect in imgi2 is likely caused by a relaxation of excitation pressures in developing plastids by factors contributed by gi2, including enhanced rates of photosynthesis and increased resistance to oxidative stress. Interestingly, the suppression phenotype of imgi can be mimicked by crossing im with the starch accumulation mutant, starch excess1 (sex1), perhaps because sex1 utilizes pathways similar to gi. We conclude that our studies provide a direct genetic linkage between GI and chloroplast biogenesis, and we construct a model of interactions between signaling pathways mediated by gi, GA, SPY, cytokinins, and sex1 that are required for chloroplast biogenesis.

Impaired Chloroplast Biogenesis in Immutans, an Arabidopsis Variegation Mutant, Modifies Developmental Programming, Cell Wall Composition and Resistance to Pseudomonas syringae

“…This observation confirms previous findings that white, but not green, im sectors generate ROS [ 33 ]. This raises the possibility that ROS accumulation, either directly or indirectly, affects plastid viability, division and/or size.…”

Investigating the Association between Flowering Time and Defense in the Arabidopsis thaliana-Fusarium oxysporum Interaction

“…oxysporum . Further research is required to determine whether gi -mediated resistance is a due to delayed flowering or a result of a pleotrophic effect of other processes regulated by GI such as cytokinin signaling [ 89 ], sucrose signaling [ 90 ], oxidative stress response [ 91 ], salinity tolerance [ 92 ], freezing tolerance [ 93 ], drought escape response [ 74 ] or response to viral pathogens [ 94 ].…”

A Functional Connection between the Circadian Clock and Hormonal Timing in Arabidopsis

“…However, the circadian regulation appears to be independent of CK [76], which opens the possibility of a parallel function of ARR9 to its role in CK signaling. The clock- and flowering-related component GI has been recently shown to be connected with chloroplast biogenesis [77]. The regulation relies on the interaction of multiple pathways including, among others, those of CK and GA [77].…”

“…The clock- and flowering-related component GI has been recently shown to be connected with chloroplast biogenesis [77]. The regulation relies on the interaction of multiple pathways including, among others, those of CK and GA [77]. As mentioned above, the interplay of different hormone pathways and their circadian regulation is also exemplified by studies uncovering PIF4 targets, which include genes related to auxin, BR, GA, ethylene, and CK signaling pathways [56].…”

“…SPINDLY (SPY), a negative regulator of GA signaling, interacts with GI and this interaction seems to be important in the control of flowering time, circadian cotyledon movements, and hypocotyl elongation [133]. As mentioned above, this interaction might be also important in the control of chloroplast biogenesis [77]. The circadian clock is also important in the regulation of ABA- and GA-related gene expression in seeds.…”