The AtMYB60 transcription factor regulates stomatal opening by modulating oxylipin synthesis in guard cells

Stomata are epidermal pores formed by pairs of specialized guard cells, which regulate gas exchanges between the plant and the atmosphere. Modulation of transcription has emerged as an important level of regulation of stomatal activity. The AtMYB60 transcription factor was previously identified as a positive regulator of stomatal opening, although the details of its function remain unknown. Here, we propose a role for AtMYB60 as a negative modulator of oxylipins synthesis in stomata. The atmyb60-1 mutant shows reduced stomatal opening and accumulates increased levels of 12-oxo-phytodienoic acid (12-OPDA), jasmonic acid (JA) and jasmonoyl-l-isoleucine (JA-Ile) in guard cells. We provide evidence that 12-OPDA triggers stomatal closure independently of JA and cooperatively with abscisic acid (ABA) in atmyb60-1. Our study highlights the relevance of oxylipins metabolism in stomatal regulation and indicates AtMYB60 as transcriptional integrator of ABA and oxylipins responses in guard cells.

Eliciting Plant Defenses Through Herbivore-Induced Plant Volatiles’ Exposure in Sweet Peppers

Insect herbivory activates plant defense mechanisms and releases a blend of herbivore-induced plant volatiles (HIPVs). These volatile compounds may be involved in plant-plant communication and induce defense response in undamaged plants. In this work, we investigated whether the exposure of sweet pepper plants to HIPVs [(Z)-3-hexenol, (Z)-3-hexenyl acetate, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, hexyl butanoate, methyl salicylate and methyl jasmonate] activates the sweet pepper immune defense system. For this, healthy sweet pepper plants were individually exposed to the each of the above mentioned HIPVs over 48 h. The expression of jasmonic acid and salicylic acid related genes was quantified. Here, we show that all the tested volatiles induced plant defenses by upregulating the jasmonic acid and salicylic acid signaling pathway. Additionally, the response of Frankliniella occidentalis, a key sweet pepper pest, and Orius laevigatus, the main natural enemy of F. occidentalis, to HIPV-exposed sweet pepper plants were studied in a Y-tube olfactometer. Only plants exposed to (Z)-3-hexenyl propanoate and methyl salicylate repelled F. occidentalis whereas O. laevigatus showed a strong preference to plants exposed to (Z)-3-hexenol, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, methyl salicylate and methyl jasmonate. Our results show that HIPVs act as elicitors to sweet pepper plant defenses by enhancing defensive signaling pathways. We anticipate our results to be a starting point for integrating HIPVs-based approaches in sweet pepper pest management systems which may provide a sustainable strategy to manage insect pests in horticultural plants.

Application of phytohormones as attenuators of salt stress in Tropaeolum majus L. (Tropaeolaceae)

The salinity of the soil and irrigation water is one of the great challenges of agriculture. Salinity can have harmful effects on physiological processes and plant growth, including Tropaeolum majus L. (Tropaeolaceae). The application of phytohormones can be a strategy to mitigate these effects. The aim of this study was to evaluate the application of jasmonic acid, salicylic acid, cytokinin and polyamine as attenuators of salt stress in T. majus. Three levels of salt stress were used: 0 mM NaCl (no stress), 50 mM NaCl (moderate stress) and 100 mM NaCl (severe stress). Four phytohormones and a control treatment were used: control (deionized water), jasmonic acid (200 µM), salicylic acid (2 mM), cytokinin (6-benzylaminopurine – 10 µM) and polyamine (spermine – 1 mM). Growth and gas exchange parameters were evaluated. Applied in conditions of moderate salt stress, all the phytohormones were efficient in improving plant height and leaf area (except salicylic acid); cytokinin and polyamine improved the number of flowers as well as gs, A and iCE; jasmonic acid improved the stem dry mass and total dry mass. In relation to severe salt stress, applications of jasmonic acid and polyamine were efficient in improving plant height; cytokinin improved leaf dry mass as well as gs, A, E, WUE, iWUE and iCE. The application of cytokinin, polyamine and jasmonic acid can be used to mitigate moderate salt stress in T. majus.

Pathogen-Free PTI Induction with a Plant Conditioner

The effects of ELICE16INDURES, a well-known plant conditioner developed by the Research Institute for Medicinal Plants and Herbs Ltd. Budakalasz, Hungary, were studied in a soybean population. The active ingredients of the compound have been selected to help elicit general immunity in plants without pathogenic damage, thereby roborizing the healthy plant population and preparing it for possible future biotic stressors. Here we have analyzed changes in the expression levels of genes encoding enzymes involved in the catalysis of metabolic pathways that induce and regulate PAMP-triggered immunity (PTI) at two different time points and treatments. Twenty-three different enzymes were analyzed that catalyze different metabolic pathways, such as the biosyntheses of jasmonic acid, salicylic acid, ethylene, phenylpropanoid, flavonoid, and phytoalexin biosynthesis and cellular detoxification processes. Bioinformatical softwares werw used to analyze the results. It has been found that some of the primary defense mechanisms (e.g., Mitogen-Activated-Protein Kinase (MAPK) cascade, jasmonic acid biosynthesis, flavonoid and phytoalexin biosynthesis, etc.) that intensify following the attack of pathogens can be activated without the intrusion of the actual pathogen by an immunochemical. Thus, we proved that plant resistance can be artificially conditioned.