Evidence from stable-isotope labeling that catechol is an intermediate in salicylic acid catabolism in the flowers of Silene latifolia (white campion)

Salicylic Acid Modulates Volatile Organic Compound Profiles During CEVd Infection in Tomato Plants

Background:Citrus Exocortis Viroid (CEVd) is a non-coding RNA pathogen capable of infecting a wide range of plant species, despite its lack of protein-coding ability. Viroid infections induce significant alterations in various physiological and biochemical processes, particularly impacting plant metabolism. This study shows the metabolic changes upon viroid infection in tomato plants (Solanum lycopersicum var. 'MoneyMaker') exhibiting altered levels of salicylic acid (SA), a key signal molecule involved in the plant defence against this pathogen. Methods: Transgenic RNAi_S5H lines, which have the salicylic acid 5-hydroxylase gene silenced to promote SA accumulation, and NahG lines, which overexpress a salicylate hydroxylase to degrade SA into catechol and prevent its accumulation, were used to establish different SA levels in plants, resulting in varying degrees of resistance to viroid infection. The analysis was performed by using gas chromatography-mass spectrometry (GC-MS) to explore the role of volatile organic compounds (VOCs) in plant immunity against this pathogen. Results: Our results revealed distinct volatile profiles associated with plant immunity, where RNAi_S5H-resistant plants showed significantly enhanced production of monoterpenoids upon viroid infection. Moreover, viroid-susceptible NahG plants emitted a broad range of VOCs, whilst viroid-tolerant RNAi_S5H plants exhibited less variation in VOC emission. Conclusions: This study demonstrates that SA levels significantly influence metabolic responses and immunity in tomato plants infected by CEVd. The identification of differential emitted VOCs upon CEVd infection could allow the development of biomarkers for disease or strategies for disease control.

Fluorescent Probes Visualize Phytohormone: Research Status and Opportunities

Phytohormones, as crucial regulatory factors in plant growth and development, have garnered increased interest in improving crop stress resistance. It is essential to comprehend the distribution of phytohormones in plants to assess their health status and investigate their functions. This knowledge also serves as a guide for developing and using plant growth regulators. The advancement of fluorescent probe technology, along with the wide range of fluorophores and improvements in imaging methods, has made it a successful approach for monitoring phytohormones in plants. This technique has been confirmed to be effective in plants, particularly in detecting the response of fluorescent probes to phytohormones. In this Perspective, we highlight the utility of fluorescent probes in measuring and visualizing the distribution of phytohormones in plants under external stress. However, the visualization of phytohormones with high spatial resolution and the achievement of high biocompatibility in living plants have posed significant challenges for researchers. Nonetheless, there are also many untapped opportunities in this field. This paper seeks to delve into the potential for further discussion on the subject.

Catechol acetylglucose: a newly identified benzoxazinoid-regulated defensive metabolite in maize

An enormous diversity of specialized metabolites is produced in the plant kingdom, with each individual plant synthesizing thousands of these compounds. Previous research showed that benzoxazinoids, the most abundant class of specialized metabolites in maize, also function as signaling molecules by regulating the production callose as a defense response. We searched for additional benzoxazinoid-regulated specialized metabolites, characterized them, examined whether they too function in herbivore protection, and determined how Spodoptera frugiperda (fall armyworm), a prominent maize pest, copes with these metabolites. We identified catechol acetylglucose (CAG) as a benzoxazinoid-regulated metabolite that is produced from salicylic acid via catechol and catechol glucoside. Genome-wide association studies of CAG abundance identified a gene encoding a predicted acetyltransferase. Knockout of this gene resulted in maize plants that lack CAG and over-accumulate catechol glucoside. Upon tissue disruption, maize plants accumulate catechol, which inhibits S. frugiperda growth. Analysis of caterpillar frass showed that S. frugiperda detoxifies catechol by glycosylation, and the efficiency of catechol glycosylation was correlated with S. frugiperda growth on a catechol-containing diet. Thus, the success of S. frugiperda as an agricultural pest may depend partly on its ability to detoxify catechol, which is produced as a defensive metabolite by maize.

Chemistry, biosynthesis and biology of floral volatiles: roles in pollination and other functions

Covering: 2010 to 2023Floral volatiles are a chemically diverse group of plant metabolites that serve multiple functions. Their composition is shaped by environmental, ecological and evolutionary factors. This review will summarize recent advances in floral scent research from chemical, molecular and ecological perspectives. It will focus on the major chemical classes of floral volatiles, on notable new structures, and on recent discoveries regarding the biosynthesis and the regulation of volatile emission. Special attention will be devoted to the various functions of floral volatiles, not only as attractants for different types of pollinators, but also as defenses of flowers against enemies. We will also summarize recent findings on how floral volatiles are affected by abiotic stressors, such as increased temperatures and drought, and by other organisms, such as herbivores and flower-dwelling microbes. Finally, this review will indicate current research gaps, such as the very limited knowledge of the isomeric pattern of chiral compounds and its importance in interspecific interactions.

Metabolic regulation of systemic acquired resistance

Plants achieve an optimal balance between growth and defense by a fine-tuned biosynthesis and metabolic inactivation of immune-stimulating small molecules. Recent research illustrates that three common hubs are involved in the cooperative regulation of systemic acquired resistance (SAR) by the defense hormones N-hydroxypipecolic acid (NHP) and salicylic acid (SA). First, a common set of regulatory proteins is involved in their biosynthesis. Second, NHP and SA are glucosylated by the same glycosyltransferase, UGT76B1, and thereby inactivated in concert. And third, NHP confers immunity via the SA receptor NPR1 to reprogram plants at the level of transcription and primes plants for an enhanced defense capacity. An overview of SA and NHP metabolism is provided, and their contribution to long-distance signaling in SAR is discussed.

Degradation of salicylic acid to catechol in Solanaceae by SA 1-hydroxylase

The hormone salicylic acid (SA) plays crucial roles in plant defense, stress responses, and in the regulation of plant growth and development. Whereas the biosynthetic pathways and biological functions of SA have been extensively studied, SA catabolism is less well understood. In this study, we report the identification and functional characterization of an FAD/NADH-dependent SA 1-hydroxylase from tomato (Solanum lycopersicum; SlSA1H), which catalyzes the oxidative decarboxylation of SA to catechol. Transcript levels of SlSA1H were highest in stems and its expression was correlated with the formation of the methylated catechol derivatives guaiacol and veratrole. Consistent with a role in SA catabolism, SlSA1H RNAi plants accumulated lower amounts of guaiacol and failed to produce any veratrole. Two O-methyltransferases involved in the conversion of catechol to guaiacol and guaiacol to veratrole were also functionally characterized. Subcellular localization analyses revealed the cytosolic localization of this degradation pathway. Phylogenetic analysis and functional characterization of SA1H homologs from other species indicated that this type of FAD/NADH-dependent SA 1-hydroxylases evolved recently within the Solanaceae family.