Abstract:The Standardized Precipitation Index (SPI) is now widely used throughout the world in both a research and an operational mode. For arid climates, or those with a distinct dry season where zero values are common, the SPI at short time scales is lower bounded, referring to non-normally distributed in this study. In these cases, the SPI is always greater than a certain value and fails to indicate a drought occurrence. The nationwide statistics based on our study suggest that the non-normality rates are closely related to local precipitation climates. In the eastern United States, SPI values at short time scales can be used in drought/flood monitoring and research in any season, while in the western United States, because of its distinct seasonal precipitation distribution, the appropriate usage and interpretation of this index becomes complicated. This would also be the case for all arid climates. From a mathematical point of view, the non-normally distributed SPI is caused by a high probability of no-rain cases represented in the mixed distribution that is employed in the SPI construction. From a statistical point of view, the 2-parameter gamma model used to estimate the precipitation probability density function and the limited sample size in dry areas and times would also reduce the confidence of the SPI values.On the basis of the results identified within this study, we recommend that the SPI user be cautious when applying short-time-scale SPIs in arid climatic regimes, and interpret the SPI values appropriately. In dry climates, the user should focus on the duration of the drought rather than on just its severity. It is also worth noting that the SPI results from a statistical product of the input data. This character makes it difficult to link the SPI data to the physical functioning of the Earth system.

In many species, the introduction of double-stranded RNA (dsRNA) induces potent and specific gene silencing, a phenomenon called RNA interference (RNAi). RNAi is the process of sequence-specific, posttranscriptional gene silencing (PTGS) in animals and plants, mediated by dsRNA homologous to the silenced genes. In plants, PTGS is part of a defense mechanism against virus infection, and dsRNA is the pivotal factor that induces gene silencing. Here, we report an efficient method that can produce dsRNA using a bacterial prokaryotic expression system. Using the bacteriophage lambda-dependent Red recombination system, we knocked out the rnc genes of two different Escherichia coli strains and constructed three different vectors that could produce dsRNAs. This work explores the best vector/host combinations for high output of dsRNA. In the end, we found that strain M-JM109 or the M-JM109lacY mutant strain and the vector pGEM-CP480 are the best choices for producing great quantities of dsRNA. Resistance analyses and Northern blot showed that Tobacco mosaic virus infection could be inhibited by dsRNA, and the resistance was an RNA-mediated virus resistance. Our findings indicate that exogenous dsRNA could form the basis for an effective and environmentally friendly biotechnological tool that protects plants from virus infections.

WRKY transcription factors are involved in various processes, ranging from plant growth to abiotic and biotic stress responses. Group I WRKY members have been rarely reported compared with group II or III members, particularly in cotton (Gossypium hirsutum). In this study, a group I WRKY gene, namely, GhWRKY25, was cloned from cotton and characterized. Expression analysis revealed that GhWRKY25 can be induced or deduced by the treatments of abiotic stresses and multiple defense-related signaling molecules. Overexpression of GhWRKY25 in Nicotiana benthamiana reduced plant tolerance to drought stress but enhanced tolerance to salt stress. Moreover, more MDA and ROS accumulated in transgenic plants after drought treatment with lower activities of SOD, POD, and CAT. Our study further demonstrated that GhWRKY25 overexpression in plants enhanced sensitivity to the fungal pathogen Botrytis cinerea by reducing the expression of SA or ET signaling related genes and inducing the expression of genes involved in the JA signaling pathway. These results indicated that GhWRKY25 plays negative or positive roles in response to abiotic stresses, and the reduced pathogen resistance may be related to the crosstalk of the SA and JA/ET signaling pathways.

The major promoter region for the transcription of the genome of rice tungro bacilliform virus (RTBV), a newly described badnavirus, has been identified. Fragments of the RTBV genome upstream of the site of transcription initiation were isolated and tested for promoter activity using a beta-glucuronidase receptor gene (gusA). Assays of transient gusA expression were performed following introduction of the chimeric gene into protoplasts via electroporation. The chimeric RTBV-promoter: gusA gene was more active in rice protoplasts than in maize or tobacco protoplasts, but was weaker than gusA controlled by an enhanced 35S promoter from cauliflower mosaic virus. Analysis of gusA gene expression following introduction of chimeric reporter genes into intact leaves via micro-projectile bombardment indicated that the GUS activity is present primarily in vascular tissues. Transgenic rice plants carrying the chimeric gusA gene had GUS activity only in the phloem of the vascular bundles in the leaf. Tissue printing studies demonstrated that RTBV accumulates in the vascular bundles of infected rice leaves. The results of our study indicate that phloem-specific expression from the RTBV promoter is an intrinsic property of the viral promoter.

Lipid transfer proteins (LTPs), a class of small, ubiquitous proteins, play critical roles in various environmental stresses. However, their precise biological functions remain unknown. Here we isolated an extracellular matrix-localised LTP, NtLTP4, from Nicotiana tabacum. The overexpression of NtLTP4 in N. tabacum enhanced resistance to salt and drought stresses. Upon exposure to high salinity, NtLTP4-overexpressing lines (OE lines) accumulated low Na+ levels. Salt-responsive genes, including Na+/H+ exchangers (NHX1) and high-affinity K+ transporter1 (HKT1), were dramatically higher in OE lines than in wild-type lines. NtLTP4 might regulate transcription levels of NHX1 and HKT1 to alleviate the toxicity of Na+. Interestingly, OE lines enhanced the tolerance of N. tabacum to drought stress by reducing the transpiration rate. Moreover, NtLTP4 could increase reactive oxygen species (ROS)-scavenging enzyme activity and expression levels to scavenge excess ROS under drought and high salinity conditions. We used a two-hybrid yeast system and screened seven putative proteins that interact with NtLTP4 in tobacco. An MAPK member, wound-induced protein kinase, was confirmed to interact with NtLTP4 via co-immunoprecipitation and a firefly luciferase complementation imaging assay. Taken together, this is the first functional analysis of NtLTP4, and proves that NtLTP4 positively regulates salt and drought stresses in N. tabacum.