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. 2013 Feb;64(4):1145-52.
doi: 10.1093/jxb/ers398. Epub 2013 Jan 23.

Translational downregulation of RBCL is operative in the coordinated expression of Rubisco genes in senescent leaves in rice

Yuji Suzuki  1 , Amane Makino
Affiliations

Translational downregulation of RBCL is operative in the coordinated expression of Rubisco genes in senescent leaves in rice

Yuji Suzuki et al. J Exp Bot. 2013 Feb.

Erratum in

Abstract

Rubisco gene expression was examined in detail in rice (Oryza sativa L.) leaves at different positions, i.e. expanding, mature, and senescent leaves. Rubisco small subunit (RBCS) synthesis and RBCS mRNA levels were maximal in expanding leaves and gradually became lower in mature and senescent leaves, with declines in those of the large subunit (RBCL) being relatively slower. The amount of synthesized RBCL per unit level of RBCL mRNA and polysome loading of RBCL mRNA declined in senescent leaves, whereas such phenomena were not observed for RBCS. These results suggested that gene expression of RBCL is downregulated at the level of its translation when a balance between RBCL and RBCS expression is disturbed by leaf senescence. It has been suggested that RBCS protein is a positive regulator for RBCL mRNA level in expanding rice leaves, as judged from their stoichiometric relationship in RBCS transgenic rice plants. However, the ratio of the RBCL mRNA level to the amount of synthesized RBCS in senescent leaves was significantly higher than that in expanding leaves. Therefore, it is suggested that the decline in RBCL mRNA level in senescent leaves is not fully accounted for by that in the amount of synthesized RBCS. Effects of other factors such as the stability of RBCL mRNA may come into play.

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Figures

Fig. 1.
Fig. 1.
Rubisco contents (A), the amounts of synthesized RBCS (B) and RBCL (C) and the ratio between them (D) in rice leaves at different positions. The 11th, 10th and 9th leaves were young, expanding leaves, the uppermost, fully expanded mature leaves and senescent leaves, respectively. Data of the 11th leaves were taken from Suzuki and Makino (2012). Data are presented as means ± SE (n = 3). An asterisk indicates a statistically significant difference to the value of wild-type plants by Dunnet’s test (P < 0.05).
Fig. 2.
Fig. 2.
The mRNA levels of total RBCS (A) and RBCL (B) and their ratios (C) in rice leaves at different positions. The 11th, 10th and 9th leaves were young, expanding leaves, the uppermost, fully expanded mature leaves and senescent leaves, respectively. In (A), white, light gray, dark gray and black columns represent the mRNA level of OsRBCS2, 3, 4 and 5, respectively. Data of the 11th leaves were taken from Suzuki and Makino (2012). Data are presented as means ± SE (n = 3). An asterisk indicates a statistically significant difference to the value of wild-type plants by Dunnet’s test (P < 0.05).
Fig. 3.
Fig. 3.
Ratios of the amount of synthesized RBCS to total RBCS mRNA level (A) and the amount of synthesized RBCL to RBCL mRNA level (B). Data are taken from Figs 1 and 2. Data obtained from the young expanding 11th leaves in RBCS-sense (lines 26-8 and 35-4) and RBCS-antisense (line AS-71) rice plants (Suzuki and Makino, 2012) are also presented. Data are presented as means ±SE (n=3). An asterisk indicates a statistically significant difference compared with the value of wild-type plants by Dunnet’s test (P <0.05).
Fig. 4.
Fig. 4.
Polysome loading profile of Rubisco genes in rice leaves at different positions after fractionation using sucrose gradient. The 11th, 10th and 9th leaves were young, expanding leaves, the uppermost, fully expanded mature leaves and senescent leaves, respectively. Panels (A) to (E) represent the results for OsRBCS2, 3, 4 and 5 and RBCL, respectively. In (F), distribution of total RNA among the fractions is presented. The mRNA and total RNA levels of each fraction are expressed as percentages of the sum of all fractions. Symbols are the same as in Fig. 3. Data of the 11th leaves were taken from Suzuki and Makino (2012). Data are presented as means ± SE (n = 3). An asterisk indicates a statistically significant difference to the value of wild-type plants by Dunnet’s test (P < 0.05).
Fig. 5.
Fig. 5.
Relative ratios of RBCL mRNA levels to the amount of synthesized RBCS. Data are taken from Figs 1 and 2. The value in the 11th leaves was defined as 1. Data obtained from young expanding 11th leaves in RBCS-sense (lines 26-8 and 35-4) and RBCS-antisense (line AS-71) rice plants (Suzuki and Makino, 2012) are also presented. Data are presented as means ±SE (n=3). An asterisk indicates a statistically significant difference compared with the value of wild-type plants by Dunnet’s test (P <0.05).
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