Availability of Rubisco Small Subunit Up-Regulates the Transcript Levels of Large Subunit for Stoichiometric Assembly of Its Holoenzyme in Rice

Abstract

Rubisco is composed of eight small subunits coded for by the nuclear RBCS multigene family and eight large subunits coded for by the rbcL gene in the plastome. For synthesis of the Rubisco holoenzyme, both genes need to be expressed coordinately. To investigate this molecular mechanism, the protein synthesis of two subunits of Rubisco was characterized in transgenic rice (Oryza sativa) plants with overexpression or antisense suppression of the RBCS gene. Total RBCS and rbcL messenger RNA (mRNA) levels and RBCS and RbcL synthesis simultaneously increased in RBCS-sense plants, although the increase in total RBCS mRNA level was greater. In RBCS-antisense plants, the levels of these mRNAs and the synthesis of the corresponding proteins declined to a similar extent. The amount of RBCS synthesized was tightly correlated with rbcL mRNA level among genotypes but not associated with changes in mRNA levels of other major chloroplast-encoded photosynthetic genes. The level of rbcL mRNA, in turn, was tightly correlated with the amount of RbcL synthesized, the molar ratio of RBCS synthesis to RbcL synthesis being identical irrespective of genotype. Polysome loading of rbcL mRNA was not changed. These results demonstrate that the availability of RBCS protein up-regulates the gene expression of rbcL primarily at the transcript level in a quantitative manner for stoichiometric assembly of Rubisco holoenzyme.

Interactive Effects of Elevated [CO2] and Water Stress on Physiological Traits and Gene Expression during Vegetative Growth in Four Durum Wheat Genotypes

“…In our study, RBCL and RBCS showed a common expression pattern (Table 5), confirming the coordinated expression of both subunits necessary for the assembly of the Rubisco holoenzyme (Suzuki and Makino, 2012). At the first sampling date, gene expression of RBCL and RBCS was down-regulated in response to elevated [CO 2 ] no matter which water regime was considered, in agreement with other wheat studies (Aranjuelo et al, 2013; Habash et al, 2014; Vicente et al, 2015b).…”

“…Chlorophyll content only increased under elevated [CO 2 ] in Mexa at the first sampling date, but the effect disappeared at the second sampling (Table 3). [CO 2 ] enrichment and water stress did not modify C content in leaves, suggesting that the decrease in N content was not simply due to N dilution caused by rapid growth (Taub and Wang, 2008). Overall, our data showed that the decrease in N content in plants grown under elevated [CO 2 ] and water stress during vegetative growth is genotypically dependent.…”

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

“…When the mRNA levels and protein synthesis of Rubisco subunits in young, expanding leaves were compared among RBCS -sense, RBCS -antisense, and wild-type plants, the RBCL mRNA level was observed to be tightly correlated not with RBCS mRNA levels but with the amount of synthesized RBCS protein (Suzuki and Makino, 2012). In contrast to tobacco, polysome loading of RBCL mRNA was relatively unaffected, even in RBCS -antisense plants.…”

Chitosan enhances rice seedling growth via gene expression network between nucleus and chloroplast

“…The overexpression of the rbcS gene slightly upregulates the gene expression of rbcL at the transcript level and enhances the amount of RuBisCo holoenzyme (Suzuki and Makino 2012). This might be expected to improve the photosynthetic efficiency of chitosan-treated rice and so facilitate the enhanced plant growth rate.…”