Si, A. | Search bioRxiv

bioRxiv2022

C4 Grasses Employ Various Strategies to Acclimate Rubisco Activase to Heat Stress

1Rising temperatures due to the current climate crisis will have devastating impacts on crop performance and resilience in the near future. One key step that limits plant photosynthetic performance under higher temperatures is the activity of the thermolabile enzyme rubisco activase (RCA). RCA is highly conserved in photosynthetic organisms, including C4 crops such as Zea mays (maize) and Sorghum bicolor (sorghum) which are crucial components of global food supply and the bioenergy sector. While rubisco is the most abundant protein on earth and responsible for carbon fixation, RCA is an essential chaperone required to remove inhibitory sugar phosphates from the active site of rubisco to allow for continued CO2 fixation. We set out to understand temperature-dependent RCA regulation in four different C4 plants, with a focus on the crop plants maize (two cultivars) and sorghum, as well as the model grass Setaria viridis (setaria). Gas exchange measurements confirm that CO2 assimilation is indeed limited by Ribulose 1,5-bisphosphate (RuBP) carboxylation in these organisms and at high temperatures. All three species express distinct sets of RCA isoforms and each species alters the isoform and proteoform abundances in response to heat; however, the changes are species-specific. In order to understand how even subtle changes in the molecular environment of the chloroplast stroma affect RCA function during heat acclimation, we examined the regulation of RCA activity directly with respect thermostability, the ratio of ADP to ATP and the concentration of Mg2+ ions. As shown previously, the activity of RCA is modulated by a combination of these variables, but surprisingly, how these biochemical environment factors affect RCA function differs vastly between the different C4 species, and differences are even apparent between different cultivars within a single species, both with respect to proteoform abundance and regulation. Our results suggest that each grass evolved different parts of the RCA regulation portfolio and we conclude that a successful engineering approach aimed at improving carbon capture in C4 grasses will need to accommodate these individual regulatory mechanisms.

plant biology↗

bioRxiv2019

Molecular signatures for inflammation vary across cancer types and correlate significantly with tumor stage, gender and vital status of patients

Cancer affects millions of individuals worldwide. One shortcoming of traditional cancer classification systems is that, even for tumors affecting a single organ, there is significant molecular heterogeneity. Precise molecular classification of tumors could be beneficial in personalizing patients therapy and predicting prognosis. To this end, here we propose to use molecular signatures to further refine cancer classification. Molecular signatures are collections of genes characterizing particular cell types, tissues or disease. Signatures can be used to interpret expression profiles from heterogeneous samples. Large collections of gene signatures have previously been cataloged in the MSigDB database. We have developed a web-based Signature Visualization Tool (SaVanT) to display signature scores in user-generated expression data. Here we have undertaken a systematic analysis of correlations between inflammatory signatures and cancer samples, to test whether inflammation can differentiate cancer types. Inflammatory response signatures were obtained from MsigDB and SaVanT and a signature score was computed for samples associated with 7 different cancer types. We first identified types of cancers that had high inflammation levels as measured by these signatures. The correlation between signature scores and metadata of these patients (gender, age at initial cancer diagnosis, cancer stage, and vital status) was then computed. We sought to evaluate correlations between inflammation with other clinical parameters and identified four cancer types that had statistically significant association (p-value < 0.05) with at least one clinical characteristic: pancreas adenocarcinoma (PAAD), cholangiocarcinoma (CHOL), kidney chromophobe (KICH), and uveal melanoma (UVM). These results may allow future studies to use these approaches to further refine cancer subtyping and ultimately treatment.

cancer biology↗