Frontiers on Recent Developments in Plant Science

Plant-derived medicines constitute a significant component of today’s human healthcare systems in industrialized as well as developing countries. Plants are capable of synthesizing a huge variety of small organic molecules, called secondary metabolites, usually composed of very complex and unique carbon skeleton structures. The abundance and diversity of secondary metabolites are coupled with wide pharmaceutical, therapeutic and medicinal values. Most of the plant derived biomedicines are widely used for recreation and stimulation (the alkaloids nicotine and cocaine; the terpene cannabinol) purposes. Considerable progress has been made in the technology of large-scale plant cell culture for the industrial production of plant-derived fine chemicals. Keeping in view of the huge world market for plant secondary metabolites, it is a challenge for biotechnologists to find techniques to produce these compounds in sufficient quantity and quality. Biotechnological intervention through micropropagation, biotransformation, and metabolic engineering can make the process quite profitable to exploit the productive potential of living cells for the production of bioactive compounds. Therefore, the increasing global demand for biomedicines can only be achieved by application of biotechnological approaches.

RNA interference mediated gene silencing is a knock down technology that brings revolution in functional genomics and has great promises for new applications of commercial value in crop improvement. Although the technology is still in its infancy and many mysteries of RNAi have yet to unfold, but the new field of RNAi based on genomics is increasingly being qualified as a fundamental paradigm shift for biotechnology and future genomics. The principle behind RNAi is that it starts with introduction of a dsDNA in cell, followed by activation of DICER gene and RISC complex, which eventually leads to loss of gene expression. An important aspect of silencing in plants is that it can be triggered locally and then spread via a mobile silencing signal. RNAi technology may be used for generating improved crop varieties in terms of disease resistance, insect resistance, enhancing nutritional qualities, shelf life and abiotic stress tolerance as a biological tool has been employed to investigate gene function in vitro and in vivo. It is also being used for regulating genes in crop plants in a very specific manner without affecting the expression of other genes, thus increasing their productivity.

Rhizobium-legume symbiosis represents a classical example of mutualism wherein, Rhizobium fixes inert nitrogen in the form of ammonia and equips it to plant; in return, plants provide shelter, mandatory source of carbon (dicarboxylic acids) and energy to the bacterium. Although nodulation is not a pre-requisite for leguminous plants but it has a selective advantage with respect to richness in protein (25%) enhancement as compared to wheat (10%). Perhaps, in symbiosis studies extra requirement for nitrogen is the key factor for selection of nitrogen fixation in legumes. Rhizobium infects leguminous host plants by way of growing root hairs to form nodules. Once specifically recognized, bacteria enter the cells of host plants through infection thread and infect its central tissue where they differentiate morphologically into nitrogen-fixing bacteroids. Important features of Rhizobium such as host-bacterium range, infection process, nodulation genes and its signaling have been elaborated. Studies on Rhizobium-legume symbiosis over the last 20 years, is gigantic, therefore, present chapter is restricted to plant-microbe interaction and its future prospects using biotechnological tools.

Metroxylon sagu (sago palm) has long been considered as one of the oldest sources of food for humans because of the presence of huge amounts of starch in its trunk. Sago palm is an important food source in Papua New Guinea, Malaysia and Indonesia. Sago palm is increasingly gaining acceptance as an important food source in southern regions of Vietnam, Thailand and the Philippines. Hence, more research efforts toward sago palm breeding and conservation are being conducted. The increasing global pressure to explore non-traditional sources of food and fuel dictates an urgent focus on sago palm (Metroxylon sagu Rottboell) biotechnology research. This paper reports the results of a starch yield assessment test among various sago palm ecotypes: spiny and non-spiny in either mesic or hydric environments to determine the most suitable sources of explants for in vitro experiments. Although non-spiny sago palms from a mesic area produced the highest mean starch yield of 64.3 kg, statistical analysis showed no significant differences in mean starch yield between the four ecotypes. An account of published reports on sago palm micropropagation is also summarized to give an overview of the status of sago palm biotechnology research. Breakthroughs in micropropagation will continue to be invaluable until a rapid method of multiplication of planting materials has been achieved.

Most higher plant species are hermaphroditic and development of efficient pollination control systems is highly desirable in maintaining economical and convenient outbreeding in plants for hybrid development. Over the last two decades, several pollination control systems have been developed by genetic-engineering of nuclear or cytoplasmic encoded genes. Some of the strategies are in practical use or ready to be used in agriculture and many of them have significant importance in future hybrid-breeding programs. For the successful application of these systems, future research should take into account efficient and economical production of male-sterile female parent lines and biosafety majors.

Jatropha gossypifolia L., popularly known as the belly-ache bush is a rich natural source of novel macrocyclic diterpenoids. Crude root and stem extracts of J. gossypifolia were tested against certain human bacterial pathogens. Among the treatments, lipophilic hexane extract of the dried roots inhibited the gram negative bacterial human pathogens Corynebacterium diphtheriae, Bacillus cereus and Proteus mirabilis. Effective inhibition (18 mm) was observed against C. diphtheriae, the activity being dose-dependent among the dilutions tested, with maximum efficacy at 500 ppm. B. cereus was resistant at lower dilutions (25-100 ppm), however, 250 and 500 ppm concentrations exhibited effective inhibition (8.5 and 9.1 mm). Marginal inhibition was observed against P. mirabilis (5.5 mm) at 500 ppm. Of the 7 column fractions tested, fraction-7 exhibited significant activity against C. diphtheriae, B. cereus, P. mirabilis, Shigella flexneri, Klebsiella aerogenes and Staphylococcus aureus. Gram-negative organisms tested, except P. mirabilis and S. flexneri, showed marginal inhibition for the crude extracts. Crystalline fraction-7 appreciably inhibited K. aerogenes and S. aureus at higher concentrations (1000, 500 and 250 ppm). X-Ray Diffraction Crystallography (XRD) analysis of the crystals confirmed that it is the known macrocyclic diterpenoid, Jatrophone, with a few other proven biological activities.

Plant pathogens pose a substantial threat to the production stability and the maintenance of quality of food, feed, fibre and now fuel. Certain bacterial strains have the capacity to prevent plant diseases in natural environments and may be used to replace chemical control measures now prevalent but potentially hazardous. Members of the genus Serratia, a gram negative bacterium which has been found to be frequently associated with rhizosphere of several plants has been studied for biocontrol mechanisms and application procedures. Some selected strains of S. plymuthica, S. marcescens and S. liquefaciens have been found to reduce disease severity to a desirable extent using specific application strategies. How Serratia achieves this ability for protection against pathogenic fungi has been discussed in detail. These strains produce antibiotics such as the red pigment prodigiosin and pyrrolnitrin. Besides they produce chitinases and siderophores which help to limit fungal growth. Regulatory processes at transcriptional and post transcriptional levels control the production of autoinducer signal molecules and the antibiotic pyrrolnitrin. Induced systemic resistance is another important mechanism involved in biological control of root pathogens by Serratia species.

Accurate identification and early detection of pathogen is a crucial step in plant disease management programmes. Conventional methods were followed, which were time consuming, relied on the interpretation of visual symptoms, culturing, laboratory identification and required extensive taxonomic expertise. Rapid development of genomic techniques has greatly simplified and has revolutionarised research in the area of life sciences. Nucleic acid- based detection methods overcome various problem associated with microscopical and immunological detection methods. DNA probes are used for the precise and accurate detection of pathogen propagules in infected tissue. DNA microarray technology is currently a new and emerging diagnostic technology for plant pathogens, when coupled with PCR results in high level of sensitivity, specificity and throughput. Dot blot hybridization, microarray, polymerase chain reaction(PCR)-based methods e.g. PCR-restriction fragment length polymorphism (PCR-RFLP), nested- PCR, multiplex-PCR, reverse-transcription-PCR (RT-PCR) etc. are the techniques being employed for the detection of major pathogens viz. tobacco mosaic tobamovirus. Introduction of real-time PCR technique has improved and simplified the methods for PCR-based diagnosis of plant pathogens. Routine application of real-time PCR and metagenomic analysis may expedite entire process of diagnosis of plant pathogens.

Abiotic stresses such as drought, high salinity and cold are common adverse environmental conditions that significantly influence plant growth and productivity worldwide. NAC domain proteins are important plant-specific transcription factors (TFs) that regulate the expression of many stress-inducible genes. They act both by an ABA-dependent or independent manner and play a critical role in improving abiotic stress tolerance of plants by interacting with cis- element present in the promoter region of various abiotic stressresponsive genes. We summarize recent studies highlighting the structural and functional characters of specific members of this family, the current knowledge on the relation between NACs and their cis-elements, with emphasis on the expression and regulation of NACs in the adaptive responses to abiotic stresses. The progress of the practical and application value of NACs in crop improvement engineering has also been discussed.

A proportion of major environmental and human health problems’ are imposed by contaminated soils and water. These natural resources are prone to contamination by both organic and inorganic contaminants. Heavy metals like Cu, Cd, Zn, As, Hg are the major inorganic contaminants. These contaminants are the result of various controlled and uncontrolled human activities like disposal of waste, mining etc. The major danger from these contaminants is their entry into human food chain because of possibility of certain plants to accumulate and translocate these contaminants to edible and harvested parts. Most of the conventional remedial technologies can be successful in certain specific situations, but, they are expensive and inhibit the soil fertility; thus subsequently causes negative impacts on the ecosystem. Different emerging phytoremediation technologies which imply the use of plants to remove or lower down the metal contamination may be used to combat the problem. This cost-effective plant-based approach to remediation takes advantage of the remarkable ability of plants to extract, sequester and detoxify pollutants. There are several types of phytoremediation viz., Phytoextraction, Phytostabilization, Rhizofiltration and Phytodegradation/Phytovolatalization. Hyperaccumulators are the best candidates for phytoremediation process. In recent years, knowledge of the physiological and molecular mechanisms of phytoremediation began to emerge together with biological and engineering strategies designed to optimize and improve phytoremediation. Transgenic plants have been developed for metal uptake, tolerance and detoxification. Genetic engineering is surely a powerful tool allowing investigating, evaluating and improving the potential of phytoremediation.