An Antisense Circular RNA Regulates Expression of RuBisCO Small Subunit Genes in Arabidopsis

Circular RNA (circRNA) is a novel class of endogenous long non-coding RNA (lncRNA) and participates in diverse physiological process in plants. From the dataset obtained by high-throughput RNA sequencing, we identified a circRNA encoded by the sense strand of the exon regions spanning two RuBisCO small subunit genes, RBCS2B and RBCS3B, in Arabidopsis thaliana. We further applied the single specific primer-polymerase chain reaction (PCR) and Sanger sequencing techniques to verify this circRNA and named it ag-circRBCS (antisense and across genic-circular RNA RBCS). Using quantitative real-time PCR (qRT-PCR), we found that ag-circRBCS shares a similar rhythmic expression pattern with other RBCS genes. The expression level of ag-circRBCS is 10–40 times lower than the expression levels of RBCS genes in the photosynthetic organs in Arabidopsis, whereas the Arabidopsis root lacked ag-circRBCS expression. Furthermore, we used the delaminated layered double hydroxide lactate nanosheets (LDH-lactate-NS) to deliver in vitro synthesized ag-circRBCS into Arabidopsis seedlings. Our results indicate that ag-circRBCS could significantly depress the expression of RBCS. Given that ag-circRBCS was expressed at low concentration in vivo, we suggest that ag-circRBCS may represent a fine-tuning mechanism to regulating the expression of RBCS genes and protein content in Arabidopsis.

Big progress for small subunits: new Rubisco mutants in Arabidopsis

This article comments on: Khumsupan P, Kozlowska MA, Orr DJ, Andreou AI, Nakayama N, Patron N, Carmo-Silva E, McCormick AJ. 2020. Generating and characterizing single- and multigene mutants of the Rubisco small subunit family in Arabidopsis. Journal of Experimental Botany 71, 5963–5975.

Effects of Overproduction of Rubisco Activase on Rubisco Content in Transgenic Rice Grown at Different N Levels

It has been reported that overproduction of Rubisco activase (RCA) in rice (Oryza sativa L.) decreased Rubisco content, resulting in declining photosynthesis. We examined the effects of RCA levels on Rubisco content using transgenic rice with overexpressed or suppressed RCA under the control of different promoters of the RCA and Rubisco small subunit (RBCS) genes. All plants were grown hydroponically with different N concentrations (0.5, 2.0 and 8.0 mM-N). In RCA overproduced plants with > 2-fold RCA content (RCA-HI lines), a 10%–20% decrease in Rubisco content was observed at 0.5 and 2.0 mM-N. In contrast, at 8.0 mM-N, Rubisco content did not change in RCA-HI lines. Conversely, in plants with 50%–60% increased RCA content (RCA-MI lines), Rubisco levels remained unchanged, regardless of N concentration. Such effects on Rubisco content were independent of the promoter that was used. In plants with RCA suppression to < 10% of the wild-type RCA content, Rubisco levels were increased at 0.5 mM-N, but were unchanged at 2.0 and 8.0 mM-N. Thus, the effects of the changes in RCA levels on Rubisco content depended on N supply. Moreover, RCA overproduction was feasible without a decrease in Rubisco content, depending on the degree of RCA production.

How protein - protein interactions contribute to pyrenoid formation in Chlamydomonas

This article comments on:Atkinson N, Velanis CN, Wunder T, Clarke DJ, Mueller-Cajar O, McCormick AJ. 2019. The pyrenoidal linker protein EPYC1 phase separates with hybrid Arabidopsis-Chlamydomonas Rubisco through interactions with the algal Rubisco small subunit. Journal of Experimental Botany, 70, 5271–5285.

The pyrenoidal linker protein EPYC1 phase separates with hybrid Arabidopsis–Chlamydomonas Rubisco through interactions with the algal Rubisco small subunit

Pyrenoid linker EPYC1 interacts with specific structures of the Rubisco small subunit. Modified plant Rubisco interacts with EPYC1 to form pyrenoid-like aggregates, a key feature of the algal CO2-concentrating mechanism.