Potato miR160 is crucial for both local and SAR responses to the late blight pathogen Phytophthora infestans and modulates antagonistic cross-talk between auxin-mediated growth and salicylic acid-mediated defense responses.
Tuberization in potato (Solanum tuberosum L.) is a complex biological phenomenon which is affected by several environmental cues, genetic factors and plant nutrition. Understanding the regulation of tuber induction is essential to devise strategies to improve tuber yield and quality. It is well established that short-day photoperiods promote tuberization, whereas long days and high-temperatures inhibit or delay tuberization. Worldwide research on this complex biological process has yielded information on the important bio-molecules (proteins, RNAs, plant growth regulators) associated with the tuberization process in potato. Key proteins involved in the regulation of tuberization include StSP6A, POTH1, StBEL5, StPHYB, StCONSTANS, Sucrose transporter StSUT4, StSP5G, etc. Biomolecules that become transported from "source to sink" have also been suggested to be important signaling candidates regulating the tuberization process in potatos. Four molecules, namely StSP6A protein, StBEL5 RNA, miR172 and GAs, have been found to be the main candidates acting as mobile signals for tuberization. These biomolecules can be manipulated (overexpressed/inhibited) for improving the tuberization in commercial varieties/cultivars of potato. In this review, information about the genes/proteins and their mechanism of action associated with the tuberization process is discussed.
RNA interference (RNAi) has proved a powerful genetic tool for silencing genes in plants. Host-induced gene silencing of pathogen genes has provided a gene knockout strategy for a wide range of biotechnological applications. The RXLR effector Avr3a gene is largely responsible for virulence of oomycete plant pathogen Phytophthora infestans. In this study, we attempted to silence the Avr3a gene of P. infestans through RNAi technology. The P. infestans inoculation resulted in lower disease progression and a reduction in pathogen load, as demonstrated by disease scoring and quantification of pathogen biomass in terms of Pi08 repetitive elements, respectively. Transgenic plants induced moderate silencing of Avr3a, and the presence and/or expression of small interfering RNAs, as determined through Northern hybridization, indicated siRNA targeted against Avr3a conferred moderate resistance to P. infestans. The single effector gene did not provide complete resistance against P. infestans. Although the Avr3a effector gene could confer moderate resistance, for complete resistance, the cumulative effect of effector genes in addition to Avr3a needs to be considered. In this study, we demonstrated that host-induced RNAi is an effective strategy for functional genomics in oomycetes.
Late blight is the most devastating disease of the potato crop that can be effectively managed by growing resistant cultivars. Introgression of resistance (R) genes/quantitative trait loci (QTLs) from the Solanum germplasm into common potato is one of the plausible approaches to breed resistant cultivars. Although the conventional method of breeding will continue to play a primary role in potato improvement, molecular marker technology is becoming one of its integral components. To achieve rapid success, from the past to recent years, several R genes/QTLs that originated from wild/cultivated Solanum species were mapped on the potato genome and a few genes were cloned using molecular approaches. As a result, molecular markers closely linked to resistance genes or QTLs offer a quicker potato breeding option through marker-assisted selection (MAS). However, limited progress has been achieved so far through MAS in potato breeding. In near future, new resistance genes/QTLs are expected to be discovered from wild Solanum gene pools and linked molecular markers would be available for MAS. This article presents an update on the development of molecular markers linked to late blight resistance genes or QTLs by utilization of Solanum species for MAS in potato.Key words: late blight -molecular marker -MAS -potato -resistance gene -Solanum species Late blight caused by the oomycete (Phytophthora infestans (Mont.) de Bary) is the most important disease of potato production worldwide. This disease caused devastating impact on humanity in the mid-1840s when severe epidemics swept through Europe and resulted in the Irish potato famine (Fry 2008). Consequently, given its significant importance, there have been concerted global efforts for more than 100 years to develop durable resistant potato cultivars against P. infestans. However, evolution of new races of P. infestans was able to conquer the past resistance genes and resulted in susceptible cultivars worldwide. Durably resistant cultivars against a range of P. infestans isolates possessing multiple resistance genes are needed today, which can be developed in less time by conventional and molecular approaches. Regardless of the fact that common potato lacks significant sources of resistance, many wild Solanum species are rich sources of resistance genes. Globally breeders exploited only a very limited scale of Solanum biodiversity in potato breeding. For example, the genetic base of modern Indian potato cultivars is limited to 49 ancestors only involving the wild species S. rybinii and S. demissum. Late blight resistance genes were introgressed from the wild species S. demissum, S. stoloniferum and the cultivated S. tuberosum subsp. andigena and S. phureja into common potato in different parts of the world (Bradshaw et al. 2006c). Thus, it necessitates potato breeders to search for new sources of resistance in wild gene pools and their faster deployment into cultivars through markerassisted selection (MAS).Conventional breeding methods are of primary importance but ar...
Groundnut is an important oilseed crop of the Indian subcontinent. Yield losses due to fungal diseases are enormous in the cultivation of this crop. Over-expression of PR proteins leads to increased resistance to pathogenic fungi in several crops. The PR protein glucanase hydrolyses a major cell-wall component, glucan, of pathogenic fungi and acts as a plant defense barrier. We report in this paper, overexpression of a tobacco glucanase in transgenic groundnut and its resistance towards Cercospora arachidicola and Aspergillus flavus. PCR, Southern and Northern hybridization confirmed stable integration and expression of the glucanase gene in groundnut transgenics. When screened for resistance against Cercospora arachidicola the transgenics showed not only reduction in the number of spots but also delay in the onset of disease. Resistance was also demonstrated against one another important pathogen of groundnut, Aspergillus flavus. The transgenics not only resisted hyphal spread but also did not accumulate aflatoxin in the seeds. The results demonstrate the potential of a PR protein from a heterologous source in developing fungal disease resistant groundnut.
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