Consuelo Medina

The grapevine guard cell-related VvMYB60 transcription factor is involved in the regulation of stomatal activity and is differentially expressed in response to ABA and osmotic stress

BackgroundUnder drought, plants accumulate the signaling hormone abscisic acid (ABA), which induces the rapid closure of stomatal pores to prevent water loss. This event is trigged by a series of signals produced inside guard cells which finally reduce their turgor. Many of these events are tightly regulated at the transcriptional level, including the control exerted by MYB proteins. In a previous study, while identifying the grapevine R2R3 MYB family, two closely related genes, VvMYB30 and VvMYB60 were found with high similarity to AtMYB60, an Arabidopsis guard cell-related drought responsive gene.ResultsPromoter-GUS transcriptional fusion assays showed that expression of VvMYB60 was restricted to stomatal guard cells and was attenuated in response to ABA. Unlike VvMYB30, VvMYB60 was able to complement the loss-of-function atmyb60-1 mutant, indicating that VvMYB60 is the only true ortholog of AtMYB60 in the grape genome. In addition, VvMYB60 was differentially regulated during development of grape organs and in response to ABA and drought-related stress conditions.ConclusionsThese results show that VvMYB60 modulates physiological responses in guard cells, leading to the possibility of engineering stomatal conductance in grapevine, reducing water loss and helping this species to tolerate drought under extreme climatic conditions.

Comparative analysis of TMV-Cg and TMV-U1 detection methods in infected Arabidopsis thaliana.

The common strain of the tobacco mosaic virus (TMV-U1), and the crucifer-infecting tobacco mosaic virus (TMV-Cg), both members of Tobamovirus genus, infect efficiently the solanaceous plants such as tomato and tobacco. The crucifer-infecting tobacco mosaic virus (TMV-Cg) also infects Arabidopsis thaliana plant, spreading systemically without causing severe symptoms. In contrast, Arabidopsis is a poor host for TMV-U1 infection. Within the past 10 years, Arabidopsis has developed into a powerful model system for studying plant-pathogen interaction. However, a detailed analysis comparing the accuracy of various viral detection methods has not been reported previously. Four detection methods were evaluated in A. thaliana (ecotype Po-1), infected with TMV-U1 or TMV-Cg. Western blots, enzyme-linked immunosorbent assay (ELISA), reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ RNA hybridization methods were used to determine viral spread at various days post inoculation (dpi) in inoculated and apical non-inoculated leaves. The detection of viral spread of TMV-U1 and TMV-Cg in Arabidopsis, using these four detection methods, supports previous studies, which demonstrate that the systemic spreads of these two viruses differ in Arabidopsis. Western blotting and ELISA detected TMV-Cg at 5dpi, and TMV-U1 at 12 dpi in systemic tissues. Viral spread was detected earlier when using RNA detection methods. Reverse transcriptase-polymerase chain reaction (RT-PCR) was very sensitive for detecting TMV-Cg in A. thaliana, but less sensitive for TMV-U1 detection. In situ RNA hybridization showed differential distribution of TMV-Cg and TMV-U1 in the inoculated leaf and systemic tissues.

Genetic and histological studies on the delayed systemic movement of Tobacco Mosaic Virus in Arabidopsis thaliana

BackgroundViral infections and their spread throughout a plant require numerous interactions between the host and the virus. While new functions of viral proteins involved in these processes have been revealed, current knowledge of host factors involved in the spread of a viral infection is still insufficient. In Arabidopsis thaliana, different ecotypes present varying susceptibilities to Tobacco mosaic virus strain U1 (TMV-U1). The rate of TMV-U1 systemic movement is delayed in ecotype Col-0 when compared with other 13 ecotypes.We followed viral movement through vascular tissue in Col-0 plants by electronic microscopy studies. In addition, the delay in systemic movement of TMV-U1 was genetically studied.ResultsTMV-U1 reaches apical leaves only after 18 days post rosette inoculation (dpi) in Col-0, whereas it is detected at 9 dpi in the Uk-4 ecotype. Genetic crosses between Col-0 and Uk-4 ecotypes, followed by analysis of viral movement in F1 and F2 populations, revealed that this delayed movement correlates with a recessive, monogenic and nuclear locus. The use of selected polymorphic markers showed that this locus, denoted DSTM1 (Delayed Systemic Tobamovirus Movement 1), is positioned on the large arm of chromosome II. Electron microscopy studies following the virions route in stems of Col-0 infected plants showed the presence of curved structures, instead of the typical rigid rods of TMV-U1. This was not observed in the case of TMV-U1 infection in Uk-4, where the observed virions have the typical rigid rod morphology.ConclusionThe presence of defectively assembled virions observed by electron microscopy in vascular tissue of Col-0 infected plants correlates with a recessive delayed systemic movement trait of TMV-U1 in this ecotype.

Analysis of local and systemic spread of the crucifer-infecting TMV-Cg virus in tobacco and several Arabidopsis thaliana ecotypes

The crucifer-infecting tobacco mosaic virus, TMV-Cg, infects Arabidopsis thaliana (L.) Heynh. efficiently without causing severe symptoms. The systemic spread of TMV-Cg in Arabidopsis was evaluated in 14ecotypes. Five days after inoculation, TMV-Cg was detected in apical leaves of 8 out of 14 ecotypes. As expected, the spread of TMV-Cg in the ecotypes tested was considerably faster than that of tobacco mosaic virus (TMV-U1). To study the participation of viral proteins in the TMV-Cg-induced infection, a complete genomic cDNA of TMV-Cg was cloned. The role of TMV-Cg movement protein in systemic spread was tested with a hybrid virus, constructed from the TMV-U1 genome and the TMV-Cg movement protein gene. Contrary to expectations, the systemic spread of this hybrid in Arabidopsis was similar to that of TMV-U1. The failure of the hybrid virus to spread at rates similar to those of TMV-Cg was not due to restrictions in local movement. In tobacco (Nicotiana tabacum L.), the hybrid virus spread efficiently and induced systemic mosaic symptoms characteristic of TMV-U1. The TMV-Cg cDNA clone provides an attractive tool to study virus-host interactions.

Improved Salinity Tolerance in Carrizo Citrange Rootstock through Overexpression of Glyoxalase System Genes

Citrus plants are widely cultivated around the world and, however, are one of the most salt stress sensitive crops. To improve salinity tolerance, transgenic Carrizo citrange rootstocks that overexpress glyoxalase I and glyoxalase II genes were obtained and their salt stress tolerance was evaluated. Molecular analysis showed high expression for both glyoxalase genes (BjGlyI and PgGlyII) in 5H03 and 5H04 lines. Under control conditions, transgenic and wild type plants presented normal morphology. In salinity treatments, the transgenic plants showed less yellowing, marginal burn in lower leaves and showed less than 40% of leaf damage compared with wild type plants. The transgenic plants showed a significant increase in the dry weight of shoot but there are no differences in the root and complete plant dry weight. In addition, a higher accumulation of chlorine is observed in the roots in transgenic line 5H03 but in shoot it was lower. Also, the wild type plant accumulated around 20% more chlorine in the shoot compared to roots. These results suggest that heterologous expression of glyoxalase system genes could enhance salt stress tolerance in Carrizo citrange rootstock and could be a good biotechnological approach to improve the abiotic stress tolerance in woody plant species.