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.     

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.     

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.     

Ectopic expression of an expansin-like B gene from wild Arachis enhances tolerance to both abiotic and biotic stresses

Plant expansins are structural cell wall-loosening proteins implicated in several developmental processes and responses to environmental constraints and pathogen infection. To date, there is limited information about the biological function of expansins-like B (EXLBs), one of the smallest and less-studied subfamilies of plant expansins. In the present study, we conducted a functional analysis of the wild Arachis AdEXLB8 gene in transgenic tobacco (Nicotiana tabacum) plants to clarify its putative role in mediating defense responses to abiotic and biotic stresses. First, its cell wall localization was confirmed in plants expressing an AdEXLB8:eGFP fusion protein, while nanomechanical assays indicated cell wall reorganization and reassembly due to AdEXLB8 overexpression without compromising the phenotype. We further demonstrated that AdEXLB8 increased tolerance not only to isolated abiotic (drought) and biotic (Sclerotinia sclerotiorum and Meloidogyne incognita) stresses but also to their combination. The jasmonate and abscisic acid signaling pathways were clearly favored in transgenic plants, showing an activated antioxidative defense system. In addition to modifications in the biomechanical properties of the cell wall, we propose that AdEXLB8 overexpression interferes with phytohormone dynamics leading to a defense primed state, which culminates in plant defense responses against isolated and combined abiotic and biotic stresses.     

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.     

Cyclic nucleotide-gated ion channel gene family in rice,identification, characterization and experimental analysis of expression response to plant hormones,biotic and abiotic stresses

Background

Cyclic nucleotide-gated channels (CNGCs) are Ca²⁺-permeable cation transport channels, which are present in both animal and plant systems. They have been implicated in the uptake of both essential and toxic cations, Ca²⁺ signaling, pathogen defense, and thermotolerance in plants. To date there has not been a genome-wide overview of the CNGC gene family in any economically important crop, including rice (Oryza sativa L.). There is an urgent need for a thorough genome-wide analysis and experimental verification of this gene family in rice.

Results

In this study, a total of 16 full length rice CNGC genes distributed on chromosomes 1–6, 9 and 12, were identified by employing comprehensive bioinformatics analyses. Based on phylogeny, the family of OsCNGCs was classified into four major groups (I-IV) and two sub-groups (IV-A and IV- B). Likewise, the CNGCs from all plant lineages clustered into four groups (I-IV), where group II was conserved in all land plants. Gene duplication analysis revealed that both chromosomal segmentation (OsCNGC1 and 2, 10 and 11, 15 and 16) and tandem duplications (OsCNGC1 and 2) significantly contributed to the expansion of this gene family. Motif composition and protein sequence analysis revealed that the CNGC specific domain “cyclic nucleotide-binding domain (CNBD)” comprises a “phosphate binding cassette” (PBC) and a “hinge” region that is highly conserved among the OsCNGCs. In addition, OsCNGC proteins also contain various other functional motifs and post-translational modification sites. We successively built a stringent motif: (LI-X(2)-[GS]-X-[FV]-X-G-[1]-ELL-X-W-X(12,22)-SA-X(2)-T-X(7)-[EQ]-AF-X-L) that recognizes the rice CNGCs specifically. Prediction of cis-acting regulatory elements in 5′ upstream sequences and expression analyses through quantitative qPCR demonstrated that OsCNGC genes were highly responsive to multiple stimuli including hormonal (abscisic acid, indoleacetic acid, kinetin and ethylene), biotic (Pseudomonas fuscovaginae and Xanthomonas oryzae pv. oryzae) and abiotic (cold) stress.

Conclusions

There are 16 CNGC genes in rice, which were probably expanded through chromosomal segmentation and tandem duplications and comprise a PBC and a “hinge” region in the CNBD domain, featured by a stringent motif. The various cis-acting regulatory elements in the upstream sequences may be responsible for responding to multiple stimuli, including hormonal, biotic and abiotic stresses.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-853) contains supplementary material, which is available to authorized users.