Using seven well-replicated Qilian juniper (Sabina przewalskii Kom.) ring-width chronologies developed at Zongwulong and Shalike Mts. in the northeastern part of the Qaidam Basin annual precipitation from previous July to current June in the recent 1000 years was reconstructed for Delingha. The reconstruction can capture 63.1% of precipitation variance and the equation was stable over time. For the reconstructed precipitation, wet periods occurred in AD1520-1633 and 1933-2001, whereas dry intervals in 1429-1519 and 1634-1741. In addition, the magnitude in precipitation variation was lower before 1430 with about 15 mm, but it increased to 30 mm during the period of 1430 to 1850. After 1850, the precipitation variance decreased again. In contrast to the increase in temperature, a decrease in annual precipitation was evident since the 1990s. The agreement in low-frequency variation between the reconstruction and the glacier accumulation and particulate content in Dunde ice cores during the recent several hundred years suggested that the precipitation reconstructed in this study was rather reliable, and represented a regional signal. This 1000-year reconstruction could benefit our understanding of climatic variation in decadal to century-scale in this region, and provide basic data to climate models and to prediction of future climate in the 21st century. Keywords: northeastern part of the Qaidam Basin, tree-ring width series of Qilian juniper, precipitation reconstruction in 1000 years.

Argonaute (AGO) family proteins are effectors of RNAi in eukaryotes. AGOs bind small RNAs and use them as guides to silence target genes or transposable elements at the transcriptional or posttranscriptional level. Eukaryotic AGO proteins share common structural and biochemical properties and function through conserved core mechanisms in RNAi pathways, yet plant AGOs have evolved specialized and diversified functions. This Review covers the general features of AGO proteins and highlights recent progress toward our understanding of the mechanisms and functions of plant AGOs.

An important component of cellular biochemistry is the concentration of proteins and nucleic acids in non-membranous compartments1,2. These biomolecular condensates are formed from processes including liquid-liquid phase separation (LLPS). The multivalent interactions necessary for LLPS have been studied extensively in vitro1,3. However, what regulates LLPS in vivo is still poorly understood. Here, we identify an in vivo regulator of LLPS through a genetic suppressor screen for loss of function of the Arabidopsis RNA-binding protein FCA. FCA contains prion-like domains that phase-separate in vitro, and exhibits behavior in vivo consistent with phase separation. The mutant screen identified a functional requirement for a coiled coil protein, FLL2, in FCA nuclear body formation. FCA reduces transcriptional read-through by promoting proximal polyadenylation at many sites in the Arabidopsis genome3,4. FLL2 was required to promote this proximal polyadenylation, but not binding of FCA to target RNA. Ectopic expression of FLL2 increased the size and number of FCA nuclear bodies. Crosslinking with formaldehyde captured in vivo interactions between FLL2, FCA and the polymerase and nuclease modules of the RNA 3’ end processing machinery. These 3’ RNA processing components were found to colocalize with FCA in the nuclear bodies in vivo. We conclude that FLL2 promotes liquid-liquid phase separation, important for dynamics of polyadenylation complexes at specific poly A sites. Our findings show that coiled coil proteins can promote LLPS, expanding our understanding of the principles governing the in vivo dynamics of liquid-like bodies.

Phenological cold/warm events recorded in Chinese historical documents are used to reconstruct, at 10-30 years' resolution, winter half-year (October to April) temperatures for the past 2000 years in the central region of eastern China. Because of the uneven spatial and temporal distribution of the phenological records, the reconstruction of the regional mean temperature involves two steps: reconstruction for individual sites within the region and calculation of the regional mean. For a single site, the reconstruction involves: identifying the difference in dates in phenological events for both historical and modern records; establishing the conversion function between the date difference and temperature change from the modern records; and converting the historical records into temperature variation. The spatial representativeness of the individual sites is studied by examining the correlation between individual sites and regional mean temperature from modern instrumental data. The correlation is then used as the basis for constructing the regional mean winter half-year temperature for the past 2000 years. From the beginning of the Christian era, climate became cooler at a rate of 0.17°C per century, and around the ad 490s temperature reached about 1°C lower than that of the present (the 1951-80 mean). Then, abruptly, temperature entered a warm epoch from the ad 570s to 1310s with a warming trend of 0.04°C per century; the peak warming was about 0.3-0.6°C higher than present for 30-year periods, but over 0.9°C warmer on a 10-year basis. After the ad 1310s, temperature decreased rapidly at a rate of 0.10°C per century; the mean temperatures of the four cold troughs were 0.6-0.9°C lower than the present, with the coldest value 1.1°C lower. Temperature has been rising rapidly during the twentieth century, especially for the period 1981-99, and the mean temperature is now 0.5°C higher than for 1951-80. The most interesting aspect over the past 2000 years has been the rapid transitions between cold and warm periods.

Abstract. Using a network of tree-ring data, we show that there had been significant growth decline in the 1920s and early 1930s throughout a wide area of northern China. This growth depression is indicative of a severe and sustained drought in the 1920s and early 1930s, which was then confirmed with a variety of historical and instrumental records including hydrological, meteorological, and documentary evidence. The 1920s drought had a devastating effect not only on agricultural productivity, hydrological resources and society in the affected areas, but also on natural vegetation, as inferred from the tree-ring network and historical records. This research offers a picture of the drought calamity during the 1920s and early 1930s in northern China, and demonstrates the potential to identify spatial anomalies of large-scale drought using tree-ring networks in the semi-arid and arid areas of northern China.

As key components in the eukaryotic gene regulatory network, microRNAs (miRNAs) themselves are regulated at the level of both metabolism and activity. To identify factors that modulate miRNA activity, we used an Arabidopsis thaliana transgenic line expressing an artificial miRNA that causes trichome clustering and performed a screen for mutants with compromised miRNA activity (cma mutants) or enhanced miRNA activity (ema mutants). From this screen, we identified two novel mutant alleles of SERRATE, which is known to be required for miRNA biogenesis and dozens of other cma and ema mutants. In this study, we analyzed ema1. SAD2/EMA1 encodes an Importin b protein. The ema1 mutation had no effects on the accumulation of miRNAs and ARGONAUTE1 (AGO1) or on their cytoplasmic and nuclear distributions. Intriguingly, we found that the miRNA effector complexes purified from ema1 contained a larger amount of miRNAs and displayed elevated mRNA cleavage activities, indicating that EMA1 modulates miRNA activity by influencing the loading of miRNAs into AGO1 complexes. These results implicate EMA1 as a negative regulator of the miRNA pathway and reveal a novel layer of miRNA activity modulation.

MicroRNAs (miRNAs) are a class of small non-coding RNAs that play important regulatory roles in gene expression in plants and animals. The biogenesis of miRNAs involves the transcription of primary miRNAs (pri-miRNAs) by RNA polymerase II (RNAPII) and subsequent processing by Dicer or Dicer-like (DCL) proteins. Here we show that the Elongator complex is involved in miRNA biogenesis in Arabidopsis. Disruption of Elongator reduces RNAPII occupancy at miRNA loci and pri-miRNA transcription. We also show that Elongator interacts with the DCL1-containing Dicing complex and lack of Elongator impairs DCL1 localization in the nuclear Dicing body. Finally, we show that pri-miRNA transcripts as well as DCL1 associate with the chromatin of miRNA genes and the chromatin association of DCL1 is compromised in the absence of Elongator. Our results suggest that Elongator functions in both transcription and processing of pri-miRNAs and probably couples these two processes.

Phenological cold/warm events recorded in Chinese historical documents are used to reconstruct, at 10-30 years' resolution, winter half-year (October to April) temperatures for the past 2000 years in the central region of eastern China. Because of the uneven spatial and temporal distribution of the phenological records, the reconstruction of the regional mean temperature involves two steps: reconstruction for individual sites within the region and calculation of the regional mean. For a single site, the reconstruction involves: identifying the difference in dates in phenological events for both historical and modern records; establishing the conversion function between the date difference and temperature change from the modern records; and converting the historical records into temperature variation. The spatial representativeness of the individual sites is studied by examining the correlation between individual sites and regional mean temperature from modern instrumental data. The correlation is then used as the basis for constructing the regional mean winter half-year temperature for the past 2000 years. From the beginning of the Christian era, climate became cooler at a rate of 0.17°C per century, and around the ad 490s temperature reached about 1°C lower than that of the present (the 1951-80 mean). Then, abruptly, temperature entered a warm epoch from the ad 570s to 1310s with a warming trend of 0.04°C per century; the peak warming was about 0.3-0.6°C higher than present for 30-year periods, but over 0.9°C warmer on a 10-year basis. After the ad 1310s, temperature decreased rapidly at a rate of 0.10°C per century; the mean temperatures of the four cold troughs were 0.6-0.9°C lower than the present, with the coldest value 1.1°C lower. Temperature has been rising rapidly during the twentieth century, especially for the period 1981-99, and the mean temperature is now 0.5°C higher than for 1951-80. The most interesting aspect over the past 2000 years has been the rapid transitions between cold and warm periods.