Low temperature is one of the most severe environmental factors that impair plant growth and agricultural production. To investigate how Thellungiella halophila, an Arabidopsis-like extremophile, adapts to cold stress, a comparative proteomic approach based on two-dimensional electrophoresis was adopted to identify proteins that changed in abundance in Thellungiella rosette leaves during short term (6 h, 2 and 5 days) and long term (24 days) exposure to cold stress. Sixty-six protein spots exhibited significant change at least at one time point and maximal cold stress induced-proteome change was found in long-term cold stress group while the minimal change was found in 6-h cold treatment group. Fifty protein spots were identified by mass spectrometry analysis. The identified proteins mainly participate in photosynthesis, RNA metabolism, defense response, energy pathway, protein synthesis, folding and degradation, cell wall and cytoskeleton and signal transduction. These proteins might work cooperatively to establish a new homeostasis under cold stress. Nearly half of the identified cold-responsive proteins were associated with various aspects of chloroplast physiology suggesting that the cold stress tolerance of T. halophila is achieved, at least partly, by regulation of chloroplast function. All protein spots involved in RNA metabolism, defense response, protein synthesis, folding and degradation were found to be upregulated markedly by cold treatment, indicating enhanced RNA metabolism, defense and protein metabolism may play crucial roles in cold tolerance mechanism in T. halophila.
Stylo has a great potential for Al3+ resistance in acidic soils through secretion of citrate from the roots. To get insight into the molecular mechanisms responsible, transcriptomic changes were investigated in the roots after treatment with T01 (−Al3+, pH6.0), T02 (−Al3+, pH4.3) and T03 (50 µM AlCl3, pH4.3). In total, 83,197 unigenes generated from 130,933 contigs were obtained. Of them, 282, 148 and 816 differentially expressed unigenes (DEGs) were revealed in T01_vs_T02, T02_vs_T03 and T01_vs_T03 comparison, respectively (FDR < 0.001, log2FC > 2). DEGs by Al3+ were related to G-proteins, diacyglycerol and inositol metabolism, calcium-signaling, transcription regulation, protein modification and transporters for detoxification of Al3+. Additionally, Al3+ facilitates citrate synthesis via modifying gene expression of pathways responsible for citrate metabolism. Overall, Al3+ resistance in stylo involves multiple strategies and enhancement of citrate anabolism. The Al3+ signal transmits through heterotrimeric G-proteins, phospholipase C, inositol triphosphate, diacylglycerol, Ca2+ and protein kinases, thereby activating transcription and anion channels in plasma membrane, and resulting in citrate secretion from stylo roots.
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The plant root is a dynamic system, which is able to respond promptly to external environmental stimuli by constantly adjusting its growth and development. A key component regulating this growth and development is the finely tuned cross-talk between the auxin and cytokinin phytohormones. The gradient distribution of auxin is not only important for the growth and development of roots, but also for root growth in various response. Recent studies have shed light on the molecular mechanisms of cytokinin-mediated regulation of local auxin biosynthesis/metabolism and redistribution in establishing active auxin gradients, resulting in cell division and differentiation in primary root tips. In this review, we focus our attention on the molecular mechanisms underlying the cytokinin-controlled auxin gradient in root tips.
Aluminium (Al) toxicity is one of the major constraint for crop production in acidic soil, and the inappropriate utilization of nitrogen fertilizer can accelerate soil acidification. Despite previous studies investigating the regulation of nitrogen forms in Al toxicity of plants, the underlying mechanism, particularly at the molecular level, remains unclear. This study aims to uncover the potentially regulatory mechanism of nitrate (NO3−) in the Al resistance of maize and Arabidopsis. NO3− conservatively improves Al resistance in maize and Arabidopsis, with nitrate‐elevated citrate synthesis and exudation potentially playing critical roles in excluding Al from the root symplast. ZmSLAH2 in maize and AtSLAH1 in Arabidopsis are essential for the regulation of citrate exudation and NO3−‐promoted Al resistance, with ZmMYB81 directly targeting the ZmSLAH2 promoter to activate its activity. Additionally, NO3− transport is necessary for NO3−‐promoted Al resistance, with ZmNRT1.1A and AtNRT1.1 potentially playing vital roles. The suppression of NO3− transport in roots by ammonium (NH4+) may inhibit NO3−‐promoted Al resistance. This study provides novel insights into the understanding of the crucial role of NO3−‐mediated signalling in the Al resistance of plants and offers guidance for nitrogen fertilization on acid soils.
N-terminal acetylation (NTA) is a highly abundant protein modification catalyzed by N-terminal acetyltransferases (NATs) in eukaryotes. However, the plant NATs and their biological functions have been poorly explored. Here we reveal that loss of function of CKRC3 and NBC-1, the auxiliary subunit (Naa25) and catalytic subunit (Naa20) of Arabidopsis NatB, respectively, led to defects in skotomorphogenesis and triple responses of ethylene. Proteome profiling and WB test revealed that the 1-amincyclopropane-1-carboxylate oxidase (ACO, catalyzing the last step of ethylene biosynthesis pathway) activity was significantly down-regulated in natb mutants, leading to reduced endogenous ethylene content. The defective phenotypes could be fully rescued by application of exogenous ethylene, but less by its precursor ACC. The present results reveal a previously unknown regulation mechanism at the co-translational protein level for ethylene homeostasis, in which the NatB-mediated NTA of ACOs render them an intracellular stability to maintain ethylene homeostasis for normal growth and responses.
In Arabidopsis, Arabidillo-1 and Arabidillo-2 have great sequence homology to Dictyostelium and metazoan β-catenin/Armadillo, which are important to animal and Dictyostelium development. Arabidillo-1 and Arabidillo-2 promote lateral root formation redundantly in Arabidopsis. Here, we showed that gibberellins (GA 3 ) has a greater inhibitory effect on lateral root growth from the null mutant arabidillo-1 than from the wild type, suggesting that the mechanism for Arabidillo-1-regulated modulation of lateral root proliferation is associated with GA 3 -metabolic or signaling pathways. Our yeast two-hybrid analysis demonstrated that Arabidillo-1 interacts with ASK2 and ASK11, and that ASK2 can bind with the F-box domain of Arabidillo-1. Therefore, Arabidillo-1 is involved in the ubiquitin/26S proteasome-mediated proteolytic pathway. Based on these results, we conclude that Arabidillo-1 can degrade some positive regulator of the GA 3 signaling pathway through selective protein degradation of ubiquitin/ 26S. Moreover, that process is believed to be the mechanism for Arabidillo-1 promotion of lateral root development in Arabidopsis.
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