Effects of OsRCA Overexpression on Rubisco Activation State and Photosynthesis in Maize

Improving Crop Yield through Increasing Carbon Gain and Reducing Carbon Loss

Photosynthesis is a process where solar energy is utilized to convert atmospheric CO2 into carbohydrates, which forms the basis for plant productivity. The increasing demand for food has created a global urge to enhance yield. Earlier, the plant breeding program was targeting the yield and yield-associated traits to enhance the crop yield. However, the yield cannot be further improved without improving the leaf photosynthetic rate. Hence, in this review, various strategies to enhance leaf photosynthesis were presented. The most promising strategies were the optimization of Rubisco carboxylation efficiency, the introduction of a CO2 concentrating mechanism in C3 plants, and the manipulation of photorespiratory bypasses in C3 plants, which are discussed in detail. Improving Rubisco's carboxylation efficiency is possible by engineering targets such as Rubisco subunits, chaperones, and Rubisco activase enzyme activity. Carbon-concentrating mechanisms can be introduced in C3 plants by the adoption of pyrenoid and carboxysomes, which can increase the CO2 concentration around the Rubisco enzyme. Photorespiration is the process by which the fixed carbon is lost through an oxidative process. Different approaches to reduce carbon and nitrogen loss were discussed. Overall, the potential approaches to improve the photosynthetic process and the way forward were discussed in detail.

Molecular characterization and expression pattern of Rubisco activase gene GhRCAβ2 in upland cotton (Gossypium hirsutum L.)

BACKGROUND

Rubisco activase (RCA) is a pivotal enzyme that can catalyse the activation of Rubisco in carbon assimilation pathway. Many studies have shown that RCA may be a potential target for genetic manipulation aimed at enhancing photosynthetic efficiency and crop yield.

OBJECTIVE

To understand the biological function of the GhRCAβ2 gene in upland cotton, we cloned the coding sequence (CDS) of the GhRCAβ2 gene and investigated its sequence features, evolutionary relationship, subcellular localization, promoter sequence and expression pattern.

METHODS

The bioinformatics tools were used to analyze the sequence features of GhRCAβ2 protein. Transient transformation of Arabidopsis mesophyll protoplasts was performed to determine the subcellular localization of the GhRCAβ2 protein. The expression pattern of the GhRCAβ2 gene was examined by analyzing transcriptome data and using the quantitative real-time PCR (qRT-PCR).

RESULTS

The full-length CDS of GhRCAβ2 was 1317 bp, and it encoded a protein with a chloroplast transit peptide. The GhRCAβ2 had two conserved ATP-binding domains, and did not have the C-terminal extension (CTE) domain that was unique to the RCA α-isoform in plants. Evolutionarily, GhRCAβ2 was clustered in Group A, and had a close evolutionary relationship with the soybean RCA. Western blot analysis demonstrated that GhRCAβ2 was immunoreactive to the RCA antibody displaying a molecular weight similar to that of the RCA β-isoform. The GhRCAβ2 protein was found in chloroplast, aligning with its role as a vital enzyme in the process of photosynthesis. The GhRCAβ2 gene had a leaf tissue-specific expression pattern, and the yellow-green leaf mutant exhibited a decreased expression of GhRCAβ2 in comparison to the wild-type cotton plants. The GhRCAβ2 promoter contained several cis-acting elements that respond to light, phytohormones and stress, suggesting that the expression of GhRCAβ2 may be regulated by these factors. An additional examination of stress response indicated that GhRCAβ2 expression was influenced by cold, heat, salt, and drought stress. Notably, diverse expression pattern was observed across different stress conditions. Additionally, low phosphorus and low potassium stress may result in a notable reduction in the expression of GhRCAβ2 gene.

CONCLUSION

Our findings will establish a basis for further understanding the function of the GhRCAβ2 gene, as well as providing valuable genetic knowledge to improve cotton photosynthetic efficiency and yield under challenging environmental circumstances.

Physiological Analysis of Source-Sink Relationship in Rice Genotypes with Contrasting Grain Yields

Rice is a major staple food, and, hence, doubling its productivity is critical to sustain future food security. Improving photosynthesis, source-sink relationships and grain-filling mechanisms are promising traits for improvement in grain yield. To understand the source-sink relationship and grain yield, a set of contrasting rice genotypes differing in yield and biomass were studied for physiological, biochemical and gene-expression differences. The physiological and yield component traits of selected rice genotypes were analyzed in 2016 and 2017 under field conditions. This led to the categorization of genotypes as high yielding (HY) and high biomass, viz., Dular, Gontra Bidhan 3, Way Rarem, Patchai Perumal, Sahbhagi Dhan, Indira Barani Dhan-1, MTU1010, and Maudamani; while, low yielding (LY) and low biomass, viz. Anjali, Ghanteswari, Parijat, Khao Daw Tai, RKVY-104, Ghati Kamma Nangarhar, BAM4510 and BAM5850. The HY genotypes in general had relatively better values of yield component traits, higher photosynthetic rate (Pn) and chlorophyll (Chl) content. The study revealed that leaf area per plant and whole plant photosynthesis are the key traits contributing to high biomass production. We selected two good-performing (Sahbhagi Dhan and Maudamani) and two poor-performing (Ghanteswari and Parijat) rice genotypes for a detailed expression analysis of selected genes involved in photosynthesis, sucrose synthesis, transport, and starch synthesis in the leaf and starch metabolism in grain. Some of the HY genotypes had a relatively high level of expression of key photosynthesis genes, such as RbcS, RCA, FBPase, and ZEP over LY genotypes. This study suggests that traits, such as leaf area, photosynthesis and grain number, contribute to high grain yield in rice. These good-performing genotypes can be used as a donor in a breeding program aimed at high yields in rice.