Cytokinin action in response to abiotic and biotic stresses in plants

The phytohormone cytokinin was originally discovered as a regulator of cell division. Later, it was described to be involved in regulating numerous processes in plant growth and development including meristem activity, tissue patterning, and organ size. More recently, diverse functions for cytokinin in the response to abiotic and biotic stresses have been reported. Cytokinin is required for the defence against high light stress and to protect plants from a novel type of abiotic stress caused by an altered photoperiod. Additionally, cytokinin has a role in the response to temperature, drought, osmotic, salt, and nutrient stress. Similarly, the full response to certain plant pathogens and herbivores requires a functional cytokinin signalling pathway. Conversely, different types of stress impact cytokinin homeostasis. The diverse functions of cytokinin in responses to stress and crosstalk with other hormones are described. Its emerging roles as a priming agent and as a regulator of growth‐defence trade‐offs are discussed.     

Microbial rescue to plant under habitat-imposed abiotic and biotic stresses

Habitat-imposed abiotic and biotic stress is a serious condition and is also a land-degradation problem in arid and semi-arid regions, causing major problem for crop productivity. Most of the cultivable and a least half of irrigated lands around the world are severely affected by environmental stresses. However, in these conditions, there are plant populations successfully adapted and evolutionarily different in their strategy of stress tolerance. Vascular plants do not function as autonomous individuals, but house diverse communities of symbiotic microbes. The role of these microbes can no longer be ignored. Microbial interactions are critical not only for host but also for fungal survival in stressed environments. Plants benefit extensively by harboring these associated microbes; they promote plant growth and confer enhanced resistance to various pathogens by producing antibiotics. To date, improvements in plant quality, production, abiotic and biotic stress resistance, nutrient, and water use have relied largely on manipulating plant genomes by breeding and genetic modification. Increasing evidence indicates that the function of symbiotic microbes seems to parallel more than one of these characteristics.     

丛枝菌根真菌在寄主植物抵御生物和非生物胁迫中的作用

丛枝菌根真菌(arbuscular mycorrhiza fungi,AMF)是生态系统中普遍存在的土壤微生物,能与绝大多数植物形成共生关系,它在寄主植物抵御生物和非生物胁迫中所起的作用逐渐引起国内外学者的关注.论文综述了丛枝菌根真菌在植物抵御非生物胁迫(重金属污染、有机污染、盐胁迫和干旱胁迫)以及生物胁迫(致病菌和线虫侵染)中的作用,并在此基础上提出了未来该领域值得进一步研究的方向.     

Forest Saccharomyces paradoxus are robust to seasonal biotic and abiotic changes

Microorganisms are famous for adapting quickly to new environments. However, most evidence for rapid microbial adaptation comes from laboratory experiments or domesticated environments, and it is unclear how rates of adaptation scale from human‐influenced environments to the great diversity of wild microorganisms. We examined potential monthly‐scale selective pressures in the model forest yeast Saccharomyces paradoxus. Contrary to expectations of seasonal adaptation, the S. paradoxus population was stable over four seasons in the face of abiotic and biotic environmental changes. While the S. paradoxus population was diverse, including 41 unique genotypes among 192 sampled isolates, there was no correlation between S. paradoxus genotypes and seasonal environments. Consistent with observations from other S. paradoxus populations, the forest population was highly clonal and inbred. This lack of recombination, paired with population stability, implies that selection is not acting on the forest S. paradoxus population on a seasonal timescale. Saccharomyces paradoxus may instead have evolved generalism or phenotypic plasticity with regard to seasonal environmental changes long ago. Similarly, while the forest population included diversity among phenotypes related to intraspecific interference competition, there was no evidence for active coevolution among these phenotypes. At least ten percent of the forest S. paradoxus individuals produced “killer toxins,” which kill sensitive Saccharomyces cells, but the presence of a toxin‐producing isolate did not predict resistance to the toxin among nearby isolates. How forest yeasts acclimate to changing environments remains an open question, and future studies should investigate the physiological responses that allow microbial cells to cope with environmental fluctuations in their native habitats.     

SUMO proteins grapple with biotic and abiotic stresses in Arabidopsis

The small ubiquitin-like modifier, i.e., SUMO, utilizes conjugation and deconjugation mechanisms that are similar to those for ubiquitination. In plants, this modifier modulates important biological processes, including growth, development, and flowering. Sumoylation has a crucial role in responses to abiotic stresses, e.g., phosphate deficiency, heat or low temperature, and drought, as well as in defenses against biotic stresses such as pathogen infection. Our review focuses on the current state of knowledge about SUMO and the functions of sumoylation related to stress responses in Arabidopsis thaliana.     

Complex molecular mechanisms determine fitness of plants to biotic and abiotic stresses

The mode of growth and development of plants does not allow them to change their habitat upon stress imposition. Through the course of evolution, plants have acquired complex molecular pathways to deal with abiotic and biotic factors to ensure their survival. The changing climatic conditions have led to unprecedented weather patterns resulting in increased crop losses. Similarly, the spread of pathogens in an era of increasing international trade has resulted in introduction and adaptation of these pathogens to new areas and cause frequent epidemics. There is an increasing need to understand the molecular mechanisms underlying stress responses in plants and envision ways to develop new crop varieties with improved features.

     

Overexpression of Arabidopsis ECERIFERUM1 promotes wax very-long-chain alkane biosynthesis and influences plant response to biotic and abiotic stresses

Land plant aerial organs are covered by a hydrophobic layer called the cuticle that serves as a waterproof barrier protecting plants against desiccation, ultraviolet radiation, and pathogens. Cuticle consists of a cutin matrix as well as cuticular waxes in which very-long-chain (VLC) alkanes are the major components, representing up to 70% of the total wax content in Arabidopsis (Arabidopsis thaliana) leaves. However, despite its major involvement in cuticle formation, the alkane-forming pathway is still largely unknown. To address this deficiency, we report here the characterization of the Arabidopsis ECERIFERUM1 (CER1) gene predicted to encode an enzyme involved in alkane biosynthesis. Analysis of CER1 expression showed that CER1 is specifically expressed in the epidermis of aerial organs and coexpressed with other genes of the alkane-forming pathway. Modification of CER1 expression in transgenic plants specifically affects VLC alkane biosynthesis: waxes of TDNA insertional mutant alleles are devoid of VLC alkanes and derivatives, whereas CER1 overexpression dramatically increases the production of the odd-carbon-numbered alkanes together with a substantial accumulation of iso-branched alkanes. We also showed that CER1 expression is induced by osmotic stresses and regulated by abscisic acid. Furthermore, CER1-overexpressing plants showed reduced cuticle permeability together with reduced soil water deficit susceptibility. However, CER1 overexpression increased susceptibility to bacterial and fungal pathogens. Taken together, these results demonstrate that CER1 controls alkane biosynthesis and is highly linked to responses to biotic and abiotic stresses.     

Genetic transformation and genes for resistance to abiotic and biotic stresses in Citrus and its related genera

Citrus is the most important tree fruit crop in the world. However, citrus production is affected by both biotic and abiotic stresses, including drought, extreme temperature, salinity, citrus canker, citrus tristeza virus, and Huanglongbing (or citrus greening), among others. These stresses can severely influence growth and development of both rootstocks and/or scions of citrus trees, thus reducing both fruit production and fruit quality. Modern advances in the tools of plant biotechnology and advances in genomics play important roles in understanding how citrus crops can cope with diseases and adverse environmental conditions. Within the last decades, much progress has been made in identifying and cloning of genes involved in resistance to biotic and abiotic stresses as well in genetic transformation of Citrus and its related genera, such as Poncirus trifoliata and Fortunella spp. In this review, we will provide information on advances and insights on genetic transformation protocols as well as availability of characterized genes involved in resistance to both abiotic and biotic stresses. This will be followed with a discussion on perspectives of future developments in this field.