Basin-Scale Control on the Phytoplankton Biomass in Lake Victoria, Africa

The relative bio-optical variability within Lake Victoria was analyzed through the spatio-temporal decomposition of a 1997–2004 dataset of remotely-sensed reflectance ratios in the visible spectral range. Results show a regular seasonal pattern with a phase shift (around 2 months) between the south and north parts of the lake. Interannual trends suggested a teleconnection between the lake dynamics and El-Niño phenomena. Both seasonal and interannual patterns were associated to conditions of light limitation for phytoplankton growth and basin-scale hydrodynamics on phytoplankton access to light. Phytoplankton blooms developed during the periods of lake surface warming and water column stability. The temporal shift apparent in the bio-optical seasonal cycles was related to the differential cooling of the lake surface by southeastern monsoon winds. North-south differences in the exposure to trade winds are supported by the orography of the Eastern Great Rift Valley. The result is that surface layer warming begins in the northern part of the lake while the formation of cool and dense water continues in the southern part. The resulting buoyancy field is sufficient to induce a lake-wide convective circulation and the tilting of the isotherms along the north-south axis. Once surface warming spreads over the whole lake, the phytoplankton bloom dynamics are subjected to the internal seiche derived from the relaxation of thermocline tilting. In 1997–98, El-Niño phenomenon weakened the monsoon wind flow which led to an increase in water column stability and a higher phytoplankton optical signal throughout the lake. This suggests that phytoplankton response to expected climate scenarios will be opposite to that proposed for nutrient-limited great lakes. The present analysis of remotely-sensed bio-optical properties in combination with environmental data provides a novel basin-scale framework for research and management strategies in Lake Victoria

Copy number variation of microRNA genes in the human genome

<p>Abstract</p> <p>Background</p> <p>MicroRNAs (miRNAs) are important genetic elements that regulate the expression of thousands of human genes. Polymorphisms affecting miRNA biogenesis, dosage and target recognition may represent potentially functional variants. The functional consequences of single nucleotide polymorphisms (SNPs) within critical miRNA sequences and outside of miRNA genes were previously demonstrated using both experimental and computational methods. However, little is known about how copy number variations (CNVs) affect miRNA genes.</p> <p>Results</p> <p>In this study, we analyzed the co-localization of all miRNA <it>loci </it>with known CNV regions. Using bioinformatic tools we identified and validated 209 copy number variable miRNA genes (CNV-miRNAs) in CNV regions deposited in Database of Genomic Variations (DGV) and 11 CNV-miRNAs in two sets of CNVs defined as highly polymorphic. We propose potential mechanisms of CNV-mediated variation of functional copies of miRNAs (dosage) for different types of CNVs overlapping miRNA genes. We also showed that, consistent with their essential biological functions, miRNA <it>loci </it>are underrepresented in highly polymorphic and well-validated CNV regions.</p> <p>Conclusion</p> <p>We postulate that CNV-miRNAs are potential functional variants and should be considered high priority candidate variants in genotype-phenotype association studies.</p

Rice early flowering1, a CKI, phosphorylates DELLA protein SLR1 to negatively regulate gibberellin signalling

The plant hormone gibberellin (GA) is crucial for multiple aspects of plant growth and development. To study the relevant regulatory mechanisms, we isolated a rice mutant earlier flowering1, el1, which is deficient in a casein kinase I that has critical roles in both plants and animals. el1 had an enhanced GA response, consistent with the suppression of EL1 expression by exogenous GA3. Biochemical characterization showed that EL1 specifically phosphorylates the rice DELLA protein SLR1, proving a direct evidence for SLR1 phosphorylation. Overexpression of SLR1 in wild-type plants caused a severe dwarf phenotype, which was significantly suppressed by EL1 deficiency, indicating the negative effect of SLR1 on GA signalling requires the EL1 function. Further studies showed that the phosphorylation of SLR1 is important for maintaining its activity and stability, and mutation of the candidate phosphorylation site of SLR1 results in the altered GA signalling. This study shows EL1 a novel and key regulator of the GA response and provided important clues on casein kinase I activities in GA signalling and plant development