Plant Biology

doi: 10.1111/plb.13439pmid: N/A

Touhami, I.; Rzigui, T.; Zribi, L.; Ennajah, A.; Dhahri, S.; Aouinti, H.; Elaieb, M. T.; Fkiri, S.; Ghazghazi, H.; Khorchani, A.; Candelier, K.; Khaldi, A.; Khouja, M. L.

doi: 10.1111/plb.13524pmid: 37014233

According to the sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC), global climate change is now unequivocal. Tunisia, like many other countries, has been affected by climate changes, including rising temperatures, intense heatwaves, and altered precipitation regimes. Tunisia's mean annual temperatures has risen about +1.4 °C in the twentieth century, with the most rapid warming taking place since the 1970s. Drought represents a primary contributing factor to tree decline and dieback. Long‐term drought can result in reduced growth and health of trees, thereby increasing their susceptibility to insect pests and pathogens. Reported increases in tree mortality point toward accelerating global forest vulnerability under hotter temperatures and longer, more intense droughts. In order to assess the effect of these climate changes on the current state of forest ecosystems in Tunisia and their evolution, an investigative study was required. Here, we review the current state of knowledge on the effects of climate change on sclerophyllous and semi‐deciduous forest ecosystems in Tunisia. Natural disturbance during recent years, as well as the adaptability and resilience of some forest species to climate change, were surveyed. The Standardized Precipitation Evapotranspiration Index (SPEI) is a multi‐scalar drought index based on climate data that has been used to analyse drought variability. The SPEI time scale analysis showed a negative trend over the 1955–2021 period in Tunisian forest regions. In 2021, Tunisia lost 280 km2 of tree cover to fires, which is equivalent to 26% of the total lost area between 2008 and 2021. Changing climate conditions have also affected phenological parameters, with an advance in the start of the green season (SOS) of 9.4 days, a delay at the end of the green season (EOS) of 5 days, with a consequent extended duration of the green season (LOS) by an average of 14.2 days. All of these alarming findings invite us to seek adaptation strategies for forest ecosystems. Adapting forests to climate change is therefore a challenge for scientists as well as policymakers and managers.

Sohail, M. N.; O'Donnell, N. H.; Kaiser, B. N.; Blomstedt, C. K.; Gleadow, R. M.

doi: 10.1111/plb.13522pmid: 36992539

The cyanogenic glucoside, dhurrin, present in Sorghum bicolor is thought to have multiple functions, including in defence against herbivory. The hormone methyl jasmonate (MeJA) is also induced by herbivory and is key to instigating defence processes in plants. To investigate whether dhurrin is induced in response to herbivore attack and also to the associated presence of MeJA, sorghum plants were either wounded or exogenous MeJA was applied. We show that specific wounding (pin board and perforation) and the application of MeJA increases dhurrin concentration in leaves and sheath tissue 12 h after treatment. Quantitative PCR shows that the expression of two genes, SbCYP79A1 and SbUGT85B1, involved in the synthesis of dhurrin are significantly induced by exogenous MeJA and by wounding. Analysis of 2 kb of sequence upstream of the start codon of SbCYP79A1 identifies several cis‐acting elements that have been linked to MeJA induction. A promoter deletion series, coupled to GFP, and transiently expressed in Nicotiana benthamiana suggests that there are potentially three sequence motifs (~−925 to −976) involved in the binding of transcription factors that result in increased expression of SbCYP79A1 and the synthesis of dhurrin in response to MeJA.

Lewandowska, M.; Zienkiewicz, A.; Feussner, K.; König, S.; Kunst, L.; Feussner, I.

doi: 10.1111/plb.13513pmid: 36800436

Triacylglycerol (TAG) plays a significant role during plant stress – it maintains lipid homeostasis. Upon wounding plants accumulate TAG, likely as a storage form of fatty acids (FAs) that originate from damaged membranes. This study asked if this process depends on the two phytohormones jasmonoyl‐isoleucine (JA‐Ile) and abscisic acid (ABA), which are involved in wound signalling. To analyse regulation of wound‐induced TAG accumulation, we used mutants deficient in JA‐Ile, with reduced ABA and the myb96 mutant, which is deficient in an ABA‐dependent transcription factor. The expression of genes involved in TAG biosynthesis, and TAG content after wounding were analysed via LC–MS and GC‐FID, plastidial lipid content in all mentioned mutant lines was also determined. The localization of newly synthesized TAG was investigated using lipid droplet staining. TAG accumulation upon wounding was confirmed as well as the fact that the newly synthesized TAG are mostly composed of polyunsaturated fatty acids. Nevertheless, all tested mutant lines were able to accumulate TAG similar to the WT. We observed differences in reduction of plastidial lipids – in WT plants this was higher than in mutant lines. Newly synthesized TAGs were stored in lipid droplets at and around the wounded area. Our results show that TAG accumulation upon wounding is not dependent on JA‐Ile or ABA. The newly synthesized TAG species are composed of unsaturated fatty acids of membrane origin, and most likely serves as a transient energy store.

Vitale, L.; Francesca, S.; Arena, C.; D'Agostino, N.; Principio, L.; Vitale, E.; Cirillo, V.; Pinto, M. C.; Barone, A.; Rigano, M. M.; Franken, P.

doi: 10.1111/plb.13518pmid: 36942418

Rising daily temperatures and water shortage are two of the major concerns in agriculture. In this work, we analysed the tolerance traits in a tomato line carrying a small region of the Solanum pennellii wild genome (IL12‐4‐SL) when grown under prolonged conditions of single and combined high temperature and water stress. When exposed to stress, IL12‐4‐SL showed higher heat tolerance than the cultivated line M82 at morphological, physiological, and biochemical levels. Moreover, under stress IL12‐4‐SL produced more flowers than M82, also characterized by higher pollen viability. In both lines, water stress negatively affected photosynthesis more than heat alone, whereas the combined stress did not further exacerbate the negative impacts of drought on this trait. Despite an observed decrease in carbon fixation, the quantum yield of PSII linear electron transport in IL12‐4‐SL was not affected by stress, thereby indicating that photochemical processes other than CO2 fixation acted to maintain the electron chain in oxidized state and prevent photodamage. The ability of IL12‐4‐SL to tolerate abiotic stress was also related to the intrinsic ability of this line to accumulate ascorbic acid. The data collected in this study clearly indicate improved tolerance to single and combined abiotic stress for IL12‐4‐SL, making this line a promising one for cultivation in a climate scenario characterized by frequent and long‐lasting heatwaves and low rainfall.

Tsitsekian, D.; Daras, G.; Templalexis, D.; Avgeri, F.; Lotos, L.; Orfanidou, C. G.; Ntoukakis, V.; Maliogka, V. I.; Rigas, S.

doi: 10.1111/plb.13515pmid: 36856454

Plants have evolved well‐tuned surveillance systems, including complex defence mechanisms, to constrain pathogens. TFs are master regulators of host molecular responses against plant pathogens. While PepMV constitutes a major threat to the global tomato production, there is still a lack of information on the key TFs that regulate host responses to this virus. A combinatorial research approach was applied relying on tomato transcriptome analysis, RT‐qPCR validation, phylogenetic classification, comparative analysis of structural features, cis‐regulatory element mining and in silico co‐expression analysis to identify a set of 11 highly responsive TFs involved in the regulation of host responses to PepMV. An endemic PepMV isolate, generating typical mosaic symptoms, modified expression of ca. 3.3% of tomato genes, resulting in 1,120 DEGs. Functional classification of 502 upregulated DEGs revealed that photosynthesis, carbon fixation and gene silencing were widely affected, whereas 618 downregulated genes had an impact mainly on plant defence and carotenoid biosynthesis. Strikingly, all 11 highly responsive TFs carried abiotic stress response cis‐regulatory elements, whereas five of them were better aligned with rice than with Arabidopsis gene homologues, suggesting that plant responses against viruses may predate divergence into monocots and dicots. Interestingly, tomato C2H2 family TFs, ZAT1‐like and ZF2, may have distinct roles in plant defence due to opposite response patterns, similar to their Arabidopsis ZAT10 and ZAT12 homologues. These highly responsive TFs provide a basis to study in‐depth molecular responses of the tomato–PepMV pathosystem, providing a perspective to better comprehend viral infections.

Zhang, W.‐H.; Zhang, Z.‐Y.; Liu, Y.; Tan, Z.‐Y.; Zhou, Q.; Lin, Y.‐Z.

doi: 10.1111/plb.13520pmid: 36971569

MicroRNAs (miRNAs) play a crucial role in the growth, development, morphogenesis, signal transduction, and stress response in plants. The ICE (Inducer of CBF expression)‐CBF (C‐repeat binding factor)‐COR (Cold‐regulated gene) regulatory cascade is an important signalling pathway in plant response to low temperature stress, and it remains unknown whether this pathway is regulated by miRNAs. In this study, high‐throughput sequencing was employed for predicting and identifying the miRNAs that were likely to target the ICE‐CBF‐COR pathway in Eucalyptus camaldulensis. A novel ICE1‐targeting miRNA, eca‐novel‐miR‐259‐5p (nov‐miR259), was further analysed. A total of 392 conserved miRNAs and 97 novel miRNAs were predicted, including 80 differentially expressed miRNAs. Of these, 30 miRNAs were predicted to be associated with the ICE‐CBF‐COR pathway. The full‐length of mature nov‐miR259 was 22 bp and its precursor gene was 60 bp in length, with a typical hairpin structure. The RNA ligase‐mediated 5′ amplification of cDNA ends (5′‐RLM‐RACE) and Agrobacterium‐mediated tobacco transient expression assays demonstrated that nov‐miR259 could cleave EcaICE1 in vivo. Moreover, qRT‐PCR and Pearson's correlation analysis further revealed that the expression levels of nov‐miR259 were almost significantly negatively correlated with those of its target gene, EcaICE1, and the other genes in the ICE‐CBF‐COR pathway. We first identified the nov‐miR259 as a novel ICE1‐targeting miRNA, and the nov‐miR259‐ICE1 module may be involved in regulating the cold stress response in E. camaldulensis.

Nagasawa, K.; Fukushima, K.; Setoguchi, H.; Katsuyama, M.; Sakaguchi, S.; Lara Romero, C.

doi: 10.1111/plb.13514pmid: 36825368

Volcanic acidification creates extreme soil conditions, where rhizotoxicity from extremely low pH (2–3) and high Al3+ strongly inhibit plant growth. C. angustisquama is a dominant extremophyte in highly acidic solfatara fields, where no other vascular plants can survive. Here we investigated the key abiotic stressor determining survival of this extremophyte. Soil analyses and topographic surveys were conducted to examine the effects of low pH and Al3+, two major abiotic stressors in acidic soils, on the occurrence of C. angustisquama in solfatara fields. Hydroponic culture experiments were also performed to test its growth responses to these stressors. In field surveys, the spatial distribution of soil pH was consistent with vegetation zonation within a solfatara field. In contrast, soil exchangeable Al content was overall low due to strong eluviation. Statistical analysis also supported the significant role of soil pH in determining the distribution of C. angustisquama in a solfatara field. Furthermore, hydroponic culture experiments revealed a higher tolerance of C. angustisquama to low pH than a sister species, especially in the range pH 2–3, corresponding to the pH values of the actual habitats of C. angustisquama. Conversely, no significant interspecific difference was detected in Al3+ tolerance, indicating that both species had high Al3+ tolerance. This study suggests that low pH is a critical abiotic stressor leading to formation of the extremophyte in highly acidic solfatara fields. In contrast, C. angustisquama displayed high tolerance to Al3+ toxicity, probably acquired prior to speciation.

Kato, Y.; Oi, T.; Taniguchi, M.

doi: 10.1111/plb.13512pmid: 36790102

C4 plants supply concentrated CO2 to bundle sheath (BS) cells, improving photosynthetic efficiency by suppressing photorespiration. Mesophyll chloroplasts in C4 plants are redistributed toward the sides of the BS cells (aggregative movement) in response to environmental stresses under light. Although this chloroplast movement is common in C4 plants, the significance and mechanisms underlying the aggregative movement remain unknown. Under environmental stresses, such as drought and salt, CO2 uptake from the atmosphere is suppressed by closing stomata to prevent water loss. We hypothesized that CO2 limitation may induce the chloroplast aggregative movement. In this study, the mesophyll chloroplast arrangement in a leaf of finger millet, an NAD‐malic enzyme type C4 plant, was examined under different CO2 concentrations and light conditions. CO2 limitation around the leaves promoted the aggregative movement, but the aggregative movement was not suppressed, even at the higher CO2 concentration than in the atmosphere, under high intensity blue light. In addition, mesophyll chloroplasts did not change their arrangement under darkness or red light. From these results, it can be concluded that CO2 limitation is not a direct inducer of the aggregative movement but would be a promoting factor of the movement under high intensity blue light.

Fuchs, B.; Saikkonen, K.; Damerau, A.; Yang, B.; Helander, M.; Pastor, V.

doi: 10.1111/plb.13517pmid: 36920172

The residues of glyphosate are found to remain in soils longer than previously reported, affecting rhizosphere microbes. This may adversely affect crop and other non‐target plants because the plant's resilience and resistance largely rely on plant‐associated microbes. Ubiquitous glyphosate residues in soil and how they impact mutualistic microbes inhabiting the aboveground plant parts are largely unexplored. We studied the effects of herbicide residues in soil on Epichloë sp., which are common endophytic symbionts inhabiting aerial parts of cool‐season grasses. In this symbiosis, the obligate symbiont subsists entirely on its host plant, and in exchange, it provides alkaloids conferring resistance to herbivores for the host grass that invests little in its own chemical defence. We first show decreased growth of Epichloë endophytes in vitro when directly exposed to two concentrations of glyphosate or glyphosate‐based herbicides. Second, we provide evidence for a reduction of Epichloë‐derived, insect‐toxic loline alkaloids in endophyte‐symbiotic meadow fescue (F. pratensis) plants growing in soil with a glyphosate history. Plants were grown for 2 years in an open field site, and natural herbivore infestation was correlated with the glyphosate‐mediated reduction of loline alkaloid concentrations. Our findings indicate that herbicides residing in soil not only affect rhizosphere microbiota but also aerial plant endophyte functionality, which emphasizes the destructive effects of glyphosate on plant symbiotic microbes, here with cascading effects on plant–pest insect interactions.