Terrestrial gross primary production (GPP) is the basis of food production and 24 vegetation growth globally 1 , and plays a critical role in regulating atmospheric CO2 through its 25 impact on ecosystem carbon balance. Even though higher CO2 concentrations in future decades 26 can increase GPP 2 , low soil water availability, heat stress, and disturbances associated with 27 droughts could reduce the benefits of such CO2 fertilization. Here we analyzed outputs of 13 28 Earth System Models (ESMs) to show an increasingly stronger impact on GPP by extreme 29 droughts than mild and moderate droughts over the 21 st century. Due to a dramatic increase in 30 the frequency of extreme droughts, the magnitude of globally-averaged reductions in GPP 31 associated with extreme droughts was projected to be nearly tripled by the last quarter of this 32 century (2075-2099) relative to that of the historical period (1850-1999) under both high and 33 intermediate greenhouse gas emission scenarios. In contrast, the magnitude of GPP reduction 34 associated with mild and moderate droughts was not projected to increase substantially. Our 35 analysis indicates a high risk of extreme droughts to the global carbon cycle with atmospheric 36 warming; however, this risk can be potentially mitigated by positive anomalies of GPP 37 associated with favorable environmental conditions. 38 39 3 The terrestrial biosphere absorbed ~30% of anthropogenic carbon emissions from fossil 40 fuels during 1990-2007 3 , making it a critical component of the global carbon sink that mitigates 41 fossil fuel CO2 emissions and associated climate warming. GPP is a measure of fixation of CO2 42 into an ecosystem through photosynthesis and plays a key role in the net carbon balance of the 43 terrestrial biosphere and the terrestrial CO2 absorption. However, despite our knowledge of CO2 44 fertilization effects on plant productivity 2 , the future trend of GPP under elevated CO2 levels 45 remains highly uncertain due to the impact of many factors such as nutrient limitation 4 and 46 increasing frequency and intensity of drought 5 . Drought is already the most widespread factor 47
A semi-mechanistic forest growth model, 3-PG (Physiological Principles Predicting Growth), was extended to calculate d
Ascomycin (FK520), a macrocyclic polyketide natural antibiotic, displays high anti-fungal and immunosuppressive activity. In this study, the LysR family transcriptional regulator FkbR1 was characterized, and its role in ascomycin biosynthesis was explored by gene deletion, complementation, and overexpression. Inactivation of fkbR1 led to 67.5% reduction of ascomycin production, which was restored by complementation of fkbR1. Overexpression of fkbR1 resulted in a 33.5% increase in ascomycin production compared with the parent strain FS35. These findings indicated that FkbR1 was a positive regulator for ascomycin production. Quantitative RT-PCR analysis revealed that the expressions of fkbE, fkbF, fkbS, and fkbU were downregulated in the fkbR1 deletion strain and upregulated in the fkbR1 overexpression strain. Electrophoretic mobility shift assays (EMSAs) in vitro and chromatin immunoprecipitation (ChIP)-qPCR assays in vivo indicated that FkbR1 bound to the intergenic region of fkbR1-fkbE. To investigate the roles of the target genes fkbE and fkbF in ascomycin production, the deletion and overexpressions of fkbE and fkbF were implemented, respectively. Overexpression of fkbE resulted in a 45.6% increase in ascomycin production, but little change was observed in fkbF overexpression strain. To further enhance ascomycin production, the fkbR1 and fkbE combinatorial overexpression strain OfkbRE was constructed with the ascomycin yield increased by 69.9% to 536.7 mg/L compared with that of the parent strain. Our research provided a helpful strategy to increase ascomycin production via engineering FkbR1 and its target gene.
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