Interactions of Gibberellins with Phytohormones and Their Role in Stress Responses

Effect of swelling agent treatment on grape fruit quality and the application of electronic nose identification detection

The swelling agent is a plant growth regulator that alters the composition and content of nutrients and volatile gases in the fruit. To identify whether grape fruit had been treated with swelling agent, the odor information and quality indexes of grape berries treated with different concentrations of swelling agent were examined by using electronic nose technology and traditional methods. The contents of soluble sugars, soluble solids, soluble proteins and vitamin C were significantly increased in N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) treated fruit. The contents of hexanal, (E)-2-hexenal, and nonanal aldehydes decreased significantly. Similarly, the levels of phenyl ethanol, 1-octanol, ethanol, and ethyl acetate alcohols and esters also decreased noticeably. Additionally, the levels of damascenone, linalool, and geraniol ketones and terpenoids decreased. However, the contents of benzaldehyde, D-limonene, acetic acid and hexanoic acid increased. In addition, the electrical signals generated by the electronic nose (e-nose) were analyzed by linear discriminant analysis (LDA), support vector machine (SVM) and random forest (RF). The average recognition rate of SVM was 94.4%. The results showed that electronic nose technology can be used to detect whether grapes have been treated with swelling agent, and it is an economical and efficient detection method.

Mendel-200: Pea as a model system to analyze hormone-mediated stem elongation

In a recent Review Article on Gregor Mendel's (1822-1884) work with pea (Pisum sativum)-plants, it was proposed that this crop species should be re-vitalized as a model organism for the study of cell- and organ growth. Here, we describe the effect of exogenous gibberellic acid (GA3) on the growth of the second internode in 4-day-old light-grown pea seedlings (Pisum sativum, large var. "Senator"). lnjection of glucose into the internode caused a growth-promoting effect similar to that of the hormone GA3. Imbibition of dry pea seeds in GA3, or water as control, resulted in a drastic enhancement in organ development in this tall variety. Similar results were reported for dwarf peas. These "classical" experimental protocols are suitable to study the elusive effect of gibberellins (which act in coordination with auxin) on the regulation of plant development at the biochemical and molecular levels.

SlWRKY16 and SlWRKY31 of tomato, negative regulators of plant defense, involved in susceptibility activation following root-knot nematode Meloidogyne javanica infection

The involvement of WRKY transcription factors in plant-nematode interactions, and in particular, how these WRKYs participate in regulating the complex morphological and physiological changes occurring after nematode infection, are the topic of active research. We characterized the functional role of the unstudied tomato WRKY genes SlWRKY16 and SlWRKY31 in regulating tomato roots' response to infection by the root-knot nematode Meloidogyne javanica. Using promoter-GUS reporter gene fusions and qRT-PCR, we show that both SlWRKYs are predominantly expressed during the first half of the parasitic life stages, when feeding-site induction and construction occur. Expression of SlWRKY16 increased sharply 15 days after inoculation, whereas SlWRKY31 was already induced earlier, but reached its maximum expression at this time. Both genes were downregulated at the mature female stage. To determine biological function, we produced transgenic lines overexpressing SlWRKY16 and SlWRKY31 in tomato hairy roots. Overexpression of both genes resulted in enhanced M. javanica infection, reflected by increased galling occurrence and reproduction. Expression profiling of marker genes responsive to defense-associated phytohormones indicated reductions in salicylic acid defense-related PR-1 and jasmonic acid defense-related PI in inoculated roots overexpressing SlWRK16 and SlWRKY31, respectively. Our results suggest that SlWRKY16 and SlWRKY31 function as negative regulators of plant immunity induced upon nematode infection.

Comparative transcriptome profiling provides insights into the growth promotion activity of Pseudomonas fluorescens strain SLU99 in tomato and potato plants

The use of biocontrol agents with plant growth-promoting activity has emerged as an approach to support sustainable agriculture. During our field evaluation of potato plants treated with biocontrol rhizobacteria, four bacteria were associated with increased plant height. Using two important solanaceous crop plants, tomato and potato, we carried out a comparative analysis of the growth-promoting activity of the four bacterial strains: Pseudomonas fluorescens SLU99, Serratia plymuthica S412, S. rubidaea AV10, and S. rubidaea EV23. Greenhouse and in vitro experiments showed that P. fluorescens SLU99 promoted plant height, biomass accumulation, and yield of potato and tomato plants, while EV23 promoted growth in potato but not in tomato plants. SLU99 induced the expression of plant hormone-related genes in potato and tomato, especially those involved in maintaining homeostasis of auxin, cytokinin, gibberellic acid and ethylene. Our results reveal potential mechanisms underlying the growth promotion and biocontrol effects of these rhizobacteria and suggest which strains may be best deployed for sustainably improving crop yield.

Genome-Wide Identification of 2-Oxoglutarate and Fe (II)-Dependent Dioxygenase (2ODD-C) Family Genes and Expression Profiles under Different Abiotic Stresses in Camellia sinensis (L.)

The 2-oxoglutarate and Fe (II)-dependent dioxygenase (2ODD-C) family of 2-oxoglutarate-dependent dioxygenases potentially participates in the biosynthesis of various metabolites under various abiotic stresses. However, there is scarce information on the expression profiles and roles of 2ODD-C genes in Camellia sinensis. We identified 153 Cs2ODD-C genes from C. sinensis, and they were distributed unevenly on 15 chromosomes. According to the phylogenetic tree topology, these genes were divided into 21 groups distinguished by conserved motifs and an intron/exon structure. Gene-duplication analyses revealed that 75 Cs2ODD-C genes were expanded and retained after WGD/segmental and tandem duplications. The expression profiles of Cs2ODD-C genes were explored under methyl jasmonate (MeJA), polyethylene glycol (PEG), and salt (NaCl) stress treatments. The expression analysis showed that 14, 13, and 49 Cs2ODD-C genes displayed the same expression pattern under MeJA and PEG treatments, MeJA and NaCl treatments, and PEG and NaCl treatments, respectively. A further analysis showed that two genes, Cs2ODD-C36 and Cs2ODD-C21, were significantly upregulated and downregulated after MeJA, PEG, and NaCl treatments, indicating that these two genes played positive and negative roles in enhancing the multi-stress tolerance. These results provide candidate genes for the use of genetic engineering technology to modify plants by enhancing multi-stress tolerance to promote phytoremediation efficiency.

GA-Mediated Disruption of RGA/BZR1 Complex Requires HSP90 to Promote Hypocotyl Elongation

Circuitries of signaling pathways integrate distinct hormonal and environmental signals, and influence development in plants. While a crosstalk between brassinosteroid (BR) and gibberellin (GA) signaling pathways has recently been established, little is known about other components engaged in the integration of the two pathways. Here, we provide supporting evidence for the role of HSP90 (HEAT SHOCK PROTEIN 90) in regulating the interplay of the GA and BR signaling pathways to control hypocotyl elongation of etiolated seedlings in Arabidopsis. Both pharmacological and genetic depletion of HSP90 alter the expression of GA biosynthesis and catabolism genes. Major components of the GA pathway, like RGA (REPRESSOR of ga1-3) and GAI (GA-INSENSITIVE) DELLA proteins, have been identified as physically interacting with HSP90. Interestingly, GA-promoted DELLA degradation depends on the ATPase activity of HSP90, and inhibition of HSP90 function stabilizes the DELLA/BZR1 (BRASSINAZOLE-RESISTANT 1) complex, modifying the expression of downstream transcriptional targets. Our results collectively reveal that HSP90, through physical interactions with DELLA proteins and BZR1, modulates DELLA abundance and regulates the expression of BZR1-dependent transcriptional targets to promote plant growth.

Plant Development and Crop Yield: The Role of Gibberellins

Gibberellins have been classically related to a few key developmental processes, thus being essential for the accurate unfolding of plant genetic programs. After more than a century of research, over one hundred different gibberellins have been described. There is a continuously increasing interest in gibberellins research because of their relevant role in the so-called "Green Revolution", as well as their current and possible applications in crop improvement. The functions attributed to gibberellins have been traditionally restricted to the regulation of plant stature, seed germination, and flowering. Nonetheless, research in the last years has shown that these functions extend to many other relevant processes. In this review, the current knowledge on gibberellins homeostasis and mode of action is briefly outlined, while specific attention is focused on the many different responses in which gibberellins take part. Thus, those genes and proteins identified as being involved in the regulation of gibberellin responses in model and non-model species are highlighted. The present review aims to provide a comprehensive picture of the state-of-the-art perception of gibberellins molecular biology and its effects on plant development. This picture might be helpful to enhance our current understanding of gibberellins biology and provide the know-how for the development of more accurate research and breeding programs.

Gibberellic acid promotes selenium accumulation in Cyphomandra betacea under selenium stress

The selenium (Se) deficiency is threatening the human health, and the increase of Se content in food can prevent the Se deficiency of human body. To increase the Se content in fruit trees and alleviate the Se stress to fruit trees, the effects of gibberellic acid (GA) on the growth and Se accumulation in Cyphomandra betacea under Se stress were studied. Although GA increased the biomass of C. betacea, it did not significantly affect the root/shoot ratio. The root and shoot biomass had a quadratic polynomial regression relationship with the GA concentration. Furthermore, GA increased the photosynthetic pigment content, photosynthetic parameters, and antioxidant enzyme activity of C. betacea. GA also increased the Se content in C. betacea, peaking at 300 mg/L GA. For instance, GA (300 mg/L) increased the Se contents in roots and shoots of C. betacea by 70.31 and 22.02%, respectively, compared with the control. Moreover, the root Se and shoot Se contents had a quadratic polynomial regression relationship with the GA concentration. Correlation and gray relational analyses showed that the carotenoid, chlorophyll a, and chlorophyll b contents were closely related to the Se uptake in C. betacea under the GA application. These results show that GA (300 mg/L) can promote the growth and Se uptake of C. betacea under Se stress.