Unusual Small Subunit That Is Not Expressed in Photosynthetic Cells Alters the Catalytic Properties of Rubisco in Rice      

Abstract

Rubisco small subunits (RbcSs) are encoded by a nuclear multigene family in plants. Five RbcS genes, OsRbcS1, OsRbcS2, OsRbcS3, OsRbcS4, and OsRbcS5, have been identified in rice (Oryza sativa). Among them, the amino acid sequence of OsRbcS1 differs notably from those of other rice RbcSs. Phylogenetic analysis showed that OsRbcS1 is genetically distant from other rice RbcS genes and more closely related to RbcS from a fern and two woody plants. Reverse transcription-PCR and promoter b-glucuronidase analyses revealed that OsRbcS1 was not expressed in leaf blade, a major photosynthetic organ in rice, but was expressed in leaf sheath, culm, anther, and root central cylinder. In leaf blade of transgenic rice overexpressing OsRbcS1 and leaf sheath of nontransgenic rice, OsRbcS1 was incorporated into the Rubisco holoenzyme. Incorporation of OsRbcS1 into Rubisco increased the catalytic turnover rate and K m for CO 2 of the enzyme and slightly decreased the specificity for CO 2 , indicating that the catalytic properties were shifted to those of a high-activity type Rubisco. The CO 2 assimilation rate at low CO 2 partial pressure was decreased in overexpression lines but was not changed under ambient and high CO 2 partial pressure compared with nontransgenic rice. Although the Rubisco content was increased, Rubisco activation state was decreased in overexpression lines. These results indicate that the catalytic properties of Rubisco can be altered by ectopic expression of OsRbcS1, with substantial effects on photosynthetic performance in rice. We believe this is the first demonstration of organ-specific expression of individual members of the RbcS gene family resulting in marked effects on Rubisco catalytic activity.

Photosynthetic Trichomes Contain a Specific Rubisco with a Modified pH-Dependent Activity

“…Except for NtRbcS-T described in this report and OsRbcS1 (Morita et al, 2014), the RbcS genes that belong to the cluster T have not been characterized so far, indicating that their expression is probably restricted to particular cell types. Nevertheless, their sequence conservation among distant species suggests that they are functional.…”

“…Recently, an unusual rice Rubisco small subunit, OsRbcS1, genetically distant from other rice RbcS sequences, has been shown to be expressed in the leaf sheath, culm, anther, and root central cylinder (Morita et al, 2014). In the phylogenetic tree, OsRbcS1 is close to NtRbcS-T, being probably part of cluster T (Fig.…”

“…The isoform examined was that showing the highest sequence identity to the "trichome" RbcS isoform from the same species. Although the rice (Oryza sativa) Rubisco small subunit, OsRbcS1, displays a BLAST score lower than the 200 threshold, its sequence and other rice RbcS sequences were added to this analysis since OsRbcS1 also exhibits a specific expression pattern (Morita et al, 2014). Because no sequence from C4 plants was obtained through the BLAST analysis, the two RbcS sequences of maize (Zea mays), a C4 plant species, were also included.…”

Rubisco Catalytic Properties and Temperature Response in Crops

“…Some of the species included in this survey, like T. aestivum, possess a large number of S-subunit genes (rbcS) encoding different S-subunits (Galili et al, 1998). Previous reports have showed that species with identical L-subunits might have different Rubisco kinetics (Rosnow et al, 2015) and directly demonstrated that differences in the S-subunits might affect Rubisco catalytic traits (Ishikawa et al, 2011;Morita et al, 2014). Therefore, we cannot reject the idea that the observed differences in Rubisco kinetics, and their temperature dependence, among the studied crops are partially due to differences in the S-subunits.…”

Surveying Rubisco diversity and temperature response to improve crop photosynthetic efficiency

“…However, advances in engineering precise changes in model systems continue to provide important developments that are increasing our understanding of Rubisco catalysis (Spreitzer et al, 2005;Whitney et al, 2011aWhitney et al, , 2011bMorita et al, 2014;Wilson et al, 2016), regulation (Andralojc et al, 2012;Carmo-Silva and Salvucci, 2013;Bracher et al, 2015), and biogenesis (Saschenbrecker et al, 2007;Whitney and Sharwood, 2008;Lin et al, 2014b;Hauser et al, 2015;Whitney et al, 2015).…”