Overexpression of a Type-A Response Regulator Alters Rice Morphology and Cytokinin Metabolism

Abstract

Genome-wide analyses of rice (Oryza sativa L.) cytokinin (CK)-responsive genes using the Affymetrix GeneChip(R) rice genome array were conducted to define the spectrum of genes subject to regulation by CK in monocotyledonous plants. Application of trans-zeatin modulated the expression of a wide variety of genes including those involved in hormone signaling and metabolism, transcriptional regulation, macronutrient transport and protein synthesis. To understand further the function of CK in rice plants, we examined the effects of in planta manipulation of a putative CK signaling factor on morphology, CK metabolism and expression of CK-responsive genes. Overexpression of the CK-inducible type-A response regulator OsRR6 abolished shoot regeneration, suggesting that OsRR6 acts as a negative regulator of CK signaling. Transgenic lines overexpressing OsRR6 (OsRR6-ox) had dwarf phenotypes with poorly developed root systems and panicles. Increased content of trans-zeatin-type CKs in OsRR6-ox lines indicates that homeostatic control of CK levels is regulated by OsRR6 signaling. Expression of genes encoding CK oxidase/dehydrogenase decreased in OsRR6-ox plants, possibly accounting for elevated CK levels in transgenic lines. Expression of a number of stress response genes was also altered in OsRR6-ox plants.

Stress-Induced Cytokinin Synthesis Increases Drought Tolerance through the Coordinated Regulation of Carbon and Nitrogen Assimilation in Rice

“…The exogenous application of CK to Arabidopsis (Arabidopsis thaliana) seedlings resulted in the reduced expression of AtNRT genes (encoding nitrate transporters) as well as some ammonium and amino acid transporters (Kiba et al, 2011). A similar CK-induced down-regulation of genes associated with nutrient acquisition was reported in 2-week-old rice seedlings grown hydroponically and treated with exogenously applied CK (Hirose et al, 2007). Since the CK-induced repression of AtNRT genes was observed under both low and high N, it was suggested that the CK effects were independent of the N status of the plant (Kiba et al, 2011).…”

Rice Cytokinin GATA Transcription Factor1 Regulates Chloroplast Development and Plant Architecture

“…While N remobilization is vitally important for grain filling, cytokinin signaling has been shown to influence rice stem length and spikelet branching and, thus, at least in part controlling yield (Ashikari et al, 2005;Hirose et al, 2007;Tabuchi et al, 2007;Zhang et al, 2010). Overexpression of Cga1 shows similar potential for increasing yield via altering panicle architecture; however, constitutive overexpression resulted in detrimental effects with respect to grain filling.…”

“…Furthermore, cytokinin signaling mediates many of the effects of applied N and can mimic these responses in the absence of N (Sakakibara, 2003;Sakakibara et al, 2006). Both cytokinin application and the modification of genes involved in cytokinin signaling influence chloroplast development, rice plant architecture, and yield (Ashikari et al, 2005;Hirose et al, 2007). As such, understanding the links between N, cytokinin, and GA signaling is also important for making improvements in agricultural crops.…”

Defining Core Metabolic and Transcriptomic Responses to Oxygen Availability in Rice Embryos and Young Seedlings

“…In order to examine transcript abundance changes across different tissues, under different conditions, and compare these with the transcript abundance profiles generated from this study, rice array data were retrieved from the Gene Expression Omnibus within the National Center for Biotechnology Information database as described previously ) with the addition of data derived from cytokinin treatment of roots and leaves (GSE6719; Hirose et al, 2007) and infection with Striga hermonthica (GSE10373; Swarbrick et al, 2008).…”