Two Rubisco activase isoforms may play different roles in photosynthetic heat acclimation in the rice plant
State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310058, China. Physiologia Plantarum
(Impact Factor: 3.14).
05/2010; 139(1):55-67. DOI: 10.1111/j.1399-3054.2009.01344.x
Studies on some plant species have shown that increasing the growth temperature gradually or pretreating with high temperature can lead to obvious photosynthetic acclimation to high temperature. To test whether this acclimation arises from heat adaptation of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 18.104.22.168) activation mediated by Rubisco activase (RCA), gene expression of RCA large isoform (RCA(L)) and RCA small isoform (RCA(S)) in rice was determined using a 4-day heat stress treatment [40/30 degrees C (day/night)] followed by a 3-day recovery under control conditions [30/22 degrees C (day/night)]. The heat stress significantly induced the expression of RCA(L) as determined by both mRNA and protein levels. Correlative analysis indicated that RCA(S) protein content was extremely significantly related to Rubisco initial activity and net photosynthetic rate (Pn) under both heat stress and normal conditions. Immunoblot analysis of the Rubisco-RCA complex revealed that the ratio of RCA(L) to Rubisco increased markedly in heat-acclimated rice leaves. Furthermore, transgenic rice plants expressing enhanced amounts of RCA(L) exhibited higher thermotolerance in Pn and Rubisco initial activity and grew better at high temperature than wild-type (WT) plants and transgenic rice plants expressing enhanced amounts of RCA(S). Under normal conditions, the transgenic rice plants expressing enhanced amounts of RCA(S) showed higher Pn and produced more biomass than transgenic rice plants expressing enhanced amounts of RCA(L) and wild-type plants. Together, these suggest that the heat-induced RCA(L) may play an important role in photosynthetic acclimation to moderate heat stress in vivo, while RCA(S) plays a major role in maintaining Rubisco initial activity under normal conditions.
Available from: Janneke Drenth
- "Rubisco activase large and small isoforms in rice are derived from the same gene by alternative splicing and there is no significant change in the total Rubisco activase mRNA level in rice during heat stress (Wang et al., 2010). Transgenic rice plants overexpressing a Rubisco activase large isoform showed higher thermotolerance than wild-type plants (Wang et al., 2010). The NCBI sequence database search and analysis revealed two Rubisco activase genes in wheat: a large isoform (TaRCA-L, AF251264) and a small isoform (TaRCA-S, DQ984669) encoded by two separate nuclear genes. "
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ABSTRACT: Heat stress is a significant environmental factor adversely affecting crop yield. Crop adaptation to high-temperature environments requires transcriptional reprogramming of a suite of genes involved in heat stress protection. This study investigated the role of TaHsfA6f, a member of the A6 subclass of heat shock transcription factors, in the regulation of heat stress protection genes in Triticum aestivum (bread wheat), a poorly understood phenomenon in this crop species. Expression analysis showed that TaHsfA6f was expressed constitutively in green organs but was markedly up-regulated during heat stress. Overexpression of TaHsfA6f in transgenic wheat using a drought-inducible promoter resulted in up-regulation of heat shock proteins (HSPs) and a number of other heat stress protection genes that included some previously unknown Hsf target genes such as Golgi anti-apoptotic protein (GAAP) and the large isoform of Rubisco activase. Transgenic wheat plants overexpressing TaHsfA6f showed improved thermotolerance. Transactivation assays showed that TaHsfA6f activated the expression of reporter genes driven by the promoters of several HSP genes (TaHSP16.8, TaHSP17, TaHSP17.3, and TaHSP90.1-A1) as well as TaGAAP and TaRof1 (a co-chaperone) under non-stress conditions. DNA binding analysis revealed the presence of high-affinity TaHsfA6f-binding heat shock element-like motifs in the promoters of these six genes. Promoter truncation and mutagenesis analyses identified TaHsfA6f-binding elements that were responsible for transactivation of TaHSP90.1-A1 and TaGAAP by TaHsfA6f. These data suggest that TaHsfA6f is a transcriptional activator that directly regulates TaHSP, TaGAAP, and TaRof1 genes in wheat and its gene regulatory network has a positive impact on thermotolerance.
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Available from: Shahniyar Bayramov
- "Also correlative analysis indicated that RCAS protein content was significantly related to Rubisco initial activity and net photosynthetic rate under both heat stress and normal conditions. Immunoblot analysis of the Rubiscoe RCA complex revealed that the ratio of RCAL to Rubisco increased markedly in heat-acclimated rice leaves (Wang et al., 2010). RCAL was upregulated in response to long-term salt stress. "
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ABSTRACT: Regulation of Rubisco (D-ribulose-1,5-bisphosphate carboxylase/oxygenase activase (RCA) gene expression and polypeptide content were determined in Brachypodium distachyon leaves, stems and ear elements at different developmental stages under optimal growth conditions as well as under drought and salt stress conditions. B. distachyon leaf contains a much greater amount of Rubisco activase small (RCAS) isoform than the large one (RCAL) under optimal growth conditions. Increased levels of the RCAL isoform compared with the RCAS isoform were found in leaves and in green stems under salt and drought stress, respectively. Transcriptional levels of RCA are almost identical in different leaf positions. Short-term drought and salt stresses did not cause the impairment of RCA gene expression in early seedlings. But gradually increasing drought stress significantly decreased gene expression in early seedling samples. Amounts of the RCAS isoform were found to be more in different leaves of the plant compared with the RCAL isoform and their ratio was constant under normal condition. In green stems gene expression of RCA decreased under salt and drought stresses, although as it was in green leaves protein amounts of RCAL isoform increased compared with the RCAS isoform. All of the above described results clearly indicate that the accumulation of each RCA isoform is differentially regulated by developmental and environmental cues.
Available from: Maoni Chao
- "Both the a and b isoforms are capable of activating Rubisco; however, they have slightly different maximal activities (Shen et al., 1991). In rice (Oryza sativa), the a isoform has been shown to play an important role in photosynthetic acclimation to moderate heat stress in vivo, whereas the b isoform has been shown to play a major role in maintaining the initial activity of Rubisco under normal conditions (Wang et al., 2010). More significantly, light modulation of Rubisco in Arabidopsis (Arabidopsis thaliana) requires a capacity for redox regulation of the a isoform via thioredoxin-f (Zhang and Portis, 1999; Zhang et al., 2001, 2002). "
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ABSTRACT: Rubisco activase (RCA) catalyzes the activation of Rubisco in vivo and plays a crucial role in regulating plant growth. In maize, only β-form RCA genes have been cloned and characterized. In this study, a genome-wide survey revealed the presence of an α-form RCA gene and a β-form RCA gene in the maize genome, herein referred to as ZmRCAα and ZmRCAβ, respectively. An analysis of genomic DNA and cDNA sequences suggested that alternative splicing of the ZmRCAβ pre-mRNA at its 3'UTR could produce two distinctive ZmRCAβ transcripts. Analyses by electrophoresis and matrix-assisted laser desorption/ionization-tandem time-of-flight mass spectrometry (MALDI-TOF-MS) showed that ZmRCAα and ZmRCAβ encode larger and smaller polypeptides of approximately 46 kD and 43 kD, respectively. Transcriptional analyses demonstrated that the expression levels of both ZmRCAα and ZmRCAβ were higher in leaves and during grain filling and that expression followed a specific cyclic day/night pattern. In 123 maize inbred lines with extensive genetic diversity, the transcript abundance and protein expression levels of these two RCA genes were positively correlated with grain yield. Additionally, both genes demonstrated a similar correlation with grain yield compared to three C4 photosynthesis genes. Our data suggest that, in addition to the β-form RCA-encoding gene, the α-form RCA-encoding gene also contributes to the synthesis of RCA in maize, and support the hypothesis that RCA genes may play an important role in determining maize productivity.
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