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This study explores how elevated carbon dioxide (CO2) levels affects the growth and defense mechanisms of plants. We focused on Aristolochia contorta Bunge (Aristolochiaceae), a wild plant that exhibits growth reduction under elevated CO2 in the previous study. The plant has Sericinus montela Gray (Papilionidae) as a specialist herbivore. By analyzing primary metabolites, understanding both the growth and defense response of plants to herbivory under elevated CO2 conditions is possible. The experiment was conducted across four groups, combining two CO2 concentration conditions (ambient CO2 and elevated CO2) with two herbivory conditions (herbivory treated and untreated). Although many plants exhibit increased growth under elevated CO2 levels, A. contorta exhibited reduced growth with lower height, dry weight, and total leaf area. Under herbivory, A. contorta triggered both localized and systemic responses. More primary metabolites exhibited significant differences due to herbivory treatment in systemic tissue than local leaves that herbivory was directly treated. Herbivory under elevated CO2 level triggered more significant responses in primary metabolites (17 metabolites) than herbivory under ambient CO2 conditions (five metabolites). Several defense-related metabolites exhibited higher concentrations in the roots and lower concentrations in the leaves in response to the herbivory treatment in the elevated CO2 group. This suggests a potential intensification of defensive responses in the underground parts of the plant under elevated CO2 levels. Our findings underscore the importance of considering both abiotic and biotic factors in understanding plant responses to environmental changes. The adaptive strategies of A. contorta suggest a complex response mechanism to elevated CO2 and herbivory pressures. [ABSTRACT FROM AUTHOR]

Lemna perpusilla and Lemna minor are free‐floating plants that often live in the same habitat. However, little is known about how they differ in response to herbivore attacks. In this study, we examined the species‐specific resistance of two Lemna species to the duckweed weevil, Tanysphyrus lemnae. The female adults of T. lemnae preferred to lay eggs on L. perpusilla over L. minor. In addition, the larvae of T. lemnae performed better when fed on L. perpusilla than on L. minor. To understand the physiological basis of species‐specific resistance in the two Lemna species, we measured the amounts of jasmonic acid (JA), phytosterols, and flavonoids. Attacks by duckweed weevils increased the levels of JA in the two Lemna species, but these levels did not differ significantly between the two species. Interestingly, the levels of flavones (isoorientin, vitexin, and isovitexin) in L. minor species were higher than those in L. perpusilla. The in vitro bioassay showed that three flavones significantly decreased the survival rate of duckweed weevil larvae. Although L. perpusilla was less resistant to duckweed weevil attack compared to L. minor, L. perpusilla grew faster than L. minor regardless of the duckweed weevil attack. These results suggest that these two Lemna species have different defense strategies against the duckweed weevil. [ABSTRACT FROM AUTHOR]

Summary: The timely removal of end‐of‐purpose flowering organs is as essential for reproduction and plant survival as timely flowering. Despite much progress in understanding the molecular mechanisms of floral organ abscission, little is known about how various environmental factors are integrated into developmental programmes that determine the timing of abscission.Here, we investigated whether reactive oxygen species (ROS), mediators of various stress‐related signalling pathways, are involved in determining the timing of abscission and, if so, how they are integrated with the developmental pathway in Arabidopsis thaliana.MSD2, encoding a secretory manganese superoxide dismutase, was preferentially expressed in the abscission zone of flowers, and floral organ abscission was accelerated by the accumulation of ROS in msd2 mutants. The expression of the genes encoding the receptor‐like kinase HAESA (HAE) and its cognate peptide ligand INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), the key signalling components of abscission, was accelerated in msd2 mutants, suggesting that MSD2 acts upstream of IDA‐HAE. Further transcriptome and pharmacological analyses revealed that abscisic acid and nitric oxide facilitate abscission by regulating the expression of IDA and HAE during MSD2‐mediated signalling.These results suggest that MSD2‐dependent ROS metabolism is an important regulatory point integrating environmental stimuli into the developmental programme leading to abscission. [ABSTRACT FROM AUTHOR]

Summary: Plants have developed tissue‐specific defense strategies in response to various herbivores with different feeding habits. Although defense responses to leaf‐chewing insects have been well studied, little is known about stem‐specific responses, particularly in the pith, to stem‐boring herbivores.To understand the stem‐specific defense, we first conducted a comparative transcriptomic analysis of the wild tobacco Nicotiana attenuata before and after attack by the leaf‐chewing herbivore Manduca sexta and the stem borer Trichobaris mucorea. When the stem‐boring herbivore attacked, lignin‐associated genes were upregulated specifically in the inner parenchymal cells of the stem, the pith; lignin also accumulated highly in the attacked pith. Silencing the lignin biosynthetic gene cinnamyl alcohol dehydrogenase enhanced the performance of the stem‐boring herbivore but had no effect on the growth of the leaf‐chewing herbivore.Two‐dimensional nuclear magnetic resonance results revealed that lignified pith contains feruloyltyramine as an unusual lignin component in the cell wall, as a response against stem‐boring herbivore attack. Pith‐specific lignification induced by the stem‐boring herbivore was modulated by both jasmonate and ethylene signaling.These results suggest that lignin provides a stem‐specific inducible barrier, protecting plants against stem‐boring insects. [ABSTRACT FROM AUTHOR]

Plants are attacked by herbivores, which often specialize on different tissues, and in response, have evolved sophisticated resistance strategies that involve different types of chemical defenses frequently targeted to different tissues. Most known phytohormones have been implicated in regulating these defenses, with jasmonates (JAs) playing a pivotal role in complex regulatory networks of signaling interactions, often generically referred to as "cross talk." The newly identified class of phytohormones, strigolactones (SLs), known to regulate the shoot architecture, remain unstudied with regard to plant–herbivore interactions. We explored the role of SL signaling in resistance to a specialist weevil (Trichobaris mucorea) herbivore of the native tobacco, Nicotiana attenuata, that attacks the root–shoot junction (RSJ), the part of the plant most strongly influenced by alterations in SL signaling (increased branching). As SL signaling shares molecular components, such as the core F-box protein more axillary growth 2 (MAX2), with another new class of phytohormones, the karrikins (KARs), which promote seed germination and seedling growth, we generated transformed lines, individually silenced in the expression of NaMAX2, dwarf 14 (NaD14: the receptor for SL) and carotenoid cleavage dioxygenase 7 (NaCCD7: a key enzyme in SL biosynthesis), and karrikin insensitive 2 (NaKAI2: the KAR receptor). The mature stems of all transgenic lines impaired in the SL, but not the KAR signaling pathway, overaccumulated anthocyanins, as did the stems of plants attacked by the larvae of weevil, which burrow into the RSJs to feed on the pith of N. attenuata stems. T. mucorea larvae grew larger in the plants silenced in the SL pathway, but again, not in the KAI2-silenced plants. These phenotypes were associated with elevated JA and auxin (indole-3-acetic acid [IAA]) levels and significant changes in the accumulation of defensive compounds, including phenolamides and nicotine. The overaccumulation of phenolamides and anthocyanins in the SL pathway–silenced plants likely resulted from antagonism between the SL and JA pathway in N. attenuata. We show that the repressors of SL signaling, suppressor of max2-like (NaSMXL6/7), and JA signaling, jasmonate zim-domain (NaJAZs), physically interact, promoting NaJAZb degradation and releasing jasmonate insensitive 1 (JIN1/MYC2) (NaMYC2), a critical transcription factor promoting JA responses. However, the increased performance of T. mucorea larvae resulted from lower pith nicotine levels, which were inhibited by increased IAA levels in SL pathway–silenced plants. This inference was confirmed by decapitation and auxin transport inhibitor treatments that decreased pith IAA and increased nicotine levels. In summary, SL signaling tunes specific sectors of specialized metabolism in stems, such as phenylpropanoid and nicotine biosynthesis, by tailoring the cross talk among phytohormones, including JA and IAA, to mediate herbivore resistance of stems. The metabolic consequences of the interplay of SL, JA, and IAA signaling revealed here could provide a mechanism for the commonly observed pattern of herbivore tolerance/resistance trade-offs. Strigolactone signaling tunes specific sectors of specialized metabolism in stems of Nicotiana attenuata, such as biosynthesis of phenopropanoids and nicotine, by tailoring cross-talk among hormones, including jasmonates and auxin, to mediate changes in plant stem pigmentation and herbivore resistance to the weevil Tricobaris mucorea. [ABSTRACT FROM AUTHOR]

Summary: Underground roots normally reside in darkness. However, they are often exposed to ambient light that penetrates through cracks in the soil layers which can occur due to wind, heavy rain or temperature extremes. In response to light exposure, roots produce reactive oxygen species (ROS) which promote root growth. It is known that ROS‐induced growth promotion facilitates rapid escape of the roots from non‐natural light. Meanwhile, long‐term exposure of the roots to light elicits a ROS burst, which causes oxidative damage to cellular components, necessitating that cellular levels of ROS should be tightly regulated in the roots. Here we demonstrate that the red/far‐red light photoreceptor phytochrome B (phyB) stimulates the biosynthesis of abscisic acid (ABA) in the shoots, and notably the shoot‐derived ABA signals induce a peroxidase‐mediated ROS detoxification reaction in the roots. Accordingly, while ROS accumulate in the roots of the phyb mutant that exhibits reduced primary root growth in the light, such an accumulation of ROS did not occur in the dark‐grown phyb roots that exhibited normal growth. These observations indicate that mobile shoot‐to‐root ABA signaling links shoot phyB‐mediated light perception with root ROS homeostasis to help roots adapt to unfavorable light exposure. We propose that ABA‐mediated shoot‐to‐root phyB signaling contributes to the synchronization of shoot and root growth for optimal propagation and performance in plants. [ABSTRACT FROM AUTHOR]

Herbivorous insects use plant metabolites to inform their host plant selection for oviposition. These host-selection behaviours are often consistent with the preference-performance hypothesis; females oviposit on hosts that maximize the performance of their offspring. However, the metabolites used for these oviposition choices and those responsible for differences in offspring performance remain unknown for ecologically relevant interactions. Here, we examined the host-selection behaviours of two sympatric weevils, the Datura ( Trichobaris compacta) and tobacco ( T. mucorea) weevils in field and glasshouse experiments with transgenic host plants specifically altered in different components of their secondary metabolism. Adult females of both species strongly preferred to feed on D. wrightii rather than on N. attenuata leaves, but T. mucorea preferred to oviposit on N. attenuata, while T. compacta oviposited only on D. wrightii. These oviposition behaviours increased offspring performance: T. compacta larvae only survived in D. wrightii stems and T. mucorea larvae survived better in N. attenuata than in D. wrightii stems. Choice assays with nicotine-free, JA-impaired, and sesquiterpene-over-produced isogenic N. attenuata plants revealed that although half of the T. compacta larvae survived in nicotine-free N. attenuata lines, nicotine did not influence the oviposition behaviours of both the nicotine-adapted and nicotine-sensitive species. JA-induced sesquiterpene volatiles are key compounds influencing T. mucorea females' oviposition choices, but these sesquiterpenes had no effect on larval performance. We conclude that adult females are able to choose the best host plant for their offspring and use chemicals different from those that influence larval performance to inform their oviposition decisions. [ABSTRACT FROM AUTHOR]

Pectobacterium brasiliense ( P. brasiliense ) is a necrotrophic bacterium that causes the soft rot disease in Brassica rapa . However, the mechanisms underlying plant immune responses against necrotrophic bacterial pathogens with a broad host range are still not well understood. Using a flg22-triggered seedling growth inhibition (SGI) assay with 455 Brassica rapa inbred lines, we selected six B. rapa flagellin-insensitive lines ( Br fin2-7) and three B. rapa flagellin-sensitive lines ( Br fs1-3). Br fin lines showed compromised flg22-induced immune responses (oxidative burst, mitogen-activated protein kinase (MAPK) activation, and seedling growth inhibition) compared to the control line R-o-18; nevertheless, they were resistant to P. brasiliense . To explain this, we analyzed the phytohormone content and found that most Br fin lines had higher P. brasiliense -induced jasmonic acid (JA) than Br fs lines. Moreover, MeJA pretreatment enhanced the resistance of B. rapa to P. brasiliense . To explain the correlation between the resistance of Br fin lines to P. brasiliense and activated JA signaling, we analyzed pathogen-induced glucosinolate (GS) content in B. rapa . Notably, in Br fin7, the neoglucobrassicin (NGBS) content among indole glucosinolates (IGS) was significantly higher than that in Br fs2 following P. brasiliense inoculation, and genes involved in IGSs biosynthesis were also highly expressed. Furthermore, almost all Br fin lines with high JA levels and resistance to P. brasiliense had higher P. brasiliense -induced NGBS levels than Br fs lines. Thus, our results show that activated JA-mediated signaling attenuates flg22-triggered immunity but enhances resistance to P. brasiliense by inducing indole glucosinolate biosynthesis in Brassica rapa . This study provides novel insights into the role of JA-mediated defense against necrotrophic bacterial pathogens within a broad host range., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Yi, Lee, Park, Lu, Lee, Kim, Kang and Lim.)