Rubisco and its regulation-major advances to improve carbon assimilation and productivity

DNA barcoding of geographical indication tagged Byadagi chilli and its cultivars using ITS2, matK and rbcL coding sequences

BACKGROUND

Byadagi chilli, a Geographical Indication (GI)-tagged chilli variety known for its special aroma and bright red colour, was accorded the GI tag in February 2011 with the GI number 129. The two traditional varieties of Byadagi chilli, namely: Dabbi and Kaddi, are the GI-tagged varieties. In this study, GI-tagged Byadagi Dabbi, Byadagi Kaddi and other cultivars of Byadagi chilli, such as Byadagi Lali (BL), Byadagi HPH 2043 (B2), Byadagi BSS 355 (B3) and another popular GI-tagged chilli variety, Guntur Sannam, were analysed to assess their inter-relationships. Due to the high market value and demand, it is important to identify and differentiate the original variety of Byadagi chilli and its associated cultivars from the other chilli cultivars, which are sold under the name of Byadagi chilli. In this study, molecular assessment by DNA barcoding was performed to establish the identity of authentic Byadagi chilli varieties.

METHODS AND RESULTS

Five samples of Byadagi chilli and another GI-tagged chilli variety, Guntur Sannam, were analysed using three DNA barcodes: ITS2, matK and rbcL. The PCR products were sequenced, nucleotide BLAST was performed and ITS2 showed 97.7% identity, matK 99.1%, and rbcL 99.19% with Capsicum annuum at the genus and species levels. Phylogenetic analysis of the DNA sequences of all the six chilli samples was performed using ClustalW multiple sequence alignment in MEGA11. The genetic distance between the six samples was calculated using the maximum likelihood approach.

CONCLUSIONS

This study distinctly demonstrates that the chloroplast DNA barcodes matK and rbcL, along with the nuclear DNA barcode, ITS2, can be used for accurate identification of Byadagi chilli cultivars. This study offers significant molecular identification and establishes a robust barcoding foundation for Byadagi chilli. The phylogenetic trees generated from the barcode sequences clearly indicated the relationships among the selected cultivars.

Radiometric determination of rubisco activation state and quantity in leaves

Rubisco is the key enzyme in photosynthesis, catalyzing fixation of carbon dioxide from the atmosphere into energy storage molecules. Several inefficiencies in Rubisco limit the rate of photosynthesis, and, therefore, the growth of the plant. Rubisco is sensitive to light, making deactivation of the enzyme upon sampling likely. Moreover, the indirect methods often used to study its activity make obtaining reliable data difficult. In this Chapter, we describe an approach to generate reliable and repeatable data for Rubisco activities, activation state and abundance in plant leaves. We include methods to sample and extract proteins, minimizing Rubisco degradation and deactivation. We describe radiometric techniques to measure Rubisco activities and calculate its activation state at the time of sampling, and to quantify its abundance.

Lighting the way: Compelling open questions in photosynthesis research

Photosynthesis-the conversion of energy from sunlight into chemical energy-is essential for life on Earth. Yet there is much we do not understand about photosynthetic energy conversion on a fundamental level: how it evolved and the extent of its diversity, its dynamics, and all the components and connections involved in its regulation. In this commentary, researchers working on fundamental aspects of photosynthesis including the light-dependent reactions, photorespiration, and C4 photosynthetic metabolism pose and discuss what they view as the most compelling open questions in their areas of research.

Transgenic expression of Rubisco accumulation factor2 and Rubisco subunits increases photosynthesis and growth in maize

Carbon assimilation by Rubisco is often a limitation to photosynthesis and therefore plant productivity. We have previously shown that transgenic co-expression of the Rubisco large (LS) and small (SS) subunits along with an essential Rubisco accumulation factor, Raf1, leads to faster growth, increased photosynthesis, and enhanced chilling tolerance in maize (Zea mays). Maize also requires Rubisco accumulation factor2 (Raf2) for full accumulation of Rubisco. Here we have analyzed transgenic maize lines with increased expression of Raf2 or Raf2 plus LS and SS. We show that increasing Raf2 expression alone had minor effects on photosynthesis, whereas expressing Raf2 with Rubisco subunits led to increased Rubisco content, more rapid carbon assimilation, and greater plant height, most notably in plants at least 6 weeks of age. The magnitude of the effects was similar to what was observed previously for expression of Raf1 together with Rubisco subunits. Taken together, this suggests that increasing the amount of either assembly factor with Rubisco subunits can independently enhance Rubisco abundance and some aspects of plant performance. These results could also imply either synergy or a degree of functional redundancy for Raf1 and Raf2, the latter of whose precise role in Rubisco assembly is currently unknown.

Altered cell wall hydroxycinnamate composition impacts leaf- and canopy-level CO2 uptake and water use in rice

Cell wall properties play a major role in determining photosynthetic carbon uptake and water use through their impact on mesophyll conductance (CO2 diffusion from substomatal cavities into photosynthetic mesophyll cells) and leaf hydraulic conductance (water movement from xylem, through leaf tissue, to stomata). Consequently, modification of cell wall (CW) properties might help improve photosynthesis and crop water use efficiency (WUE). We tested this using 2 independent transgenic rice (Oryza sativa) lines overexpressing the rice OsAT10 gene (encoding a "BAHD" CoA acyltransferase), which alters CW hydroxycinnamic acid content (more para-coumaric acid and less ferulic acid). Plants were grown under high and low water levels, and traits related to leaf anatomy, CW composition, gas exchange, hydraulics, plant biomass, and canopy-level water use were measured. Alteration of hydroxycinnamic acid content led to statistically significant decreases in mesophyll CW thickness (-14%) and increased mesophyll conductance (+120%) and photosynthesis (+22%). However, concomitant increases in stomatal conductance negated the increased photosynthesis, resulting in no change in intrinsic WUE (ratio of photosynthesis to stomatal conductance). Leaf hydraulic conductance was also unchanged; however, transgenic plants showed small but statistically significant increases in aboveground biomass (AGB) (+12.5%) and canopy-level WUE (+8.8%; ratio of AGB to water used) and performed better under low water levels than wild-type plants. Our results demonstrate that changes in CW composition, specifically hydroxycinnamic acid content, can increase mesophyll conductance and photosynthesis in C3 cereal crops such as rice. However, attempts to improve photosynthetic WUE will need to enhance mesophyll conductance and photosynthesis while maintaining or decreasing stomatal conductance.