Frontiers in Plant Science

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ISSN / EISSN : 1664-462X / 1664-462X
Published by: Frontiers Media SA (10.3389)
Total articles ≅ 16,173
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, Jožica Gričar, Jernej Jevšenak, Gregor Božič, Georg von Arx, Peter Prislan
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.669229

Abstract:
European beech (Fagus sylvatica L.) adapts to local growing conditions to enhance its performance. In response to variations in climatic conditions, beech trees adjust leaf phenology, cambial phenology, and wood formation patterns, which result in different tree-ring widths (TRWs) and wood anatomy. Chronologies of tree ring width and vessel features [i.e., mean vessel area (MVA), vessel density (VD), and relative conductive area (RCTA)] were produced for the 1960–2016 period for three sites that differ in climatic regimes and spring leaf phenology (two early- and one late-flushing populations). These data were used to investigate long-term relationships between climatic conditions and anatomical features of four quarters of tree-rings at annual and intra-annual scales. In addition, we investigated how TRW and vessel features adjust in response to extreme weather events (i.e., summer drought). We found significant differences in TRW, VD, and RCTA among the selected sites. Precipitation and maximum temperature before and during the growing season were the most important climatic factors affecting TRW and vessel characteristics. We confirmed differences in climate-growth relationships between the selected sites, late flushing beech population at Idrija showing the least pronounced response to climate. MVA was the only vessel trait that showed no relationship with TRW or other vessel features. The relationship between MVA and climatic factors evaluated at intra-annual scale indicated that vessel area in the first quarter of tree-ring were mainly influenced by climatic conditions in the previous growing season, while vessel area in the second to fourth quarters of tree ring width was mainly influenced by maximum temperature and precipitation in the current growing season. When comparing wet and dry years, beech from all sites showed a similar response, with reduced TRW and changes in intra-annual variation in vessel area. Our findings suggest that changes in temperature and precipitation regimes as predicted by most climate change scenarios will affect tree-ring increments and wood structure in beech, yet the response between sites or populations may differ.
Judith Trunschke, Klaus Lunau, Graham H. Pyke, Zong-Xin Ren,
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.617851

Abstract:
The evolution of floral traits in animal-pollinated plants involves the interaction between flowers as signal senders and pollinators as signal receivers. Flower colors are very diverse, effect pollinator attraction and flower foraging behavior, and are hypothesized to be shaped through pollinator-mediated selection. However, most of our current understanding of flower color evolution arises from variation between discrete color morphs and completed color shifts accompanying pollinator shifts, while evidence for pollinator-mediated selection on continuous variation in flower colors within populations is still scarce. In this review, we summarize experiments quantifying selection on continuous flower color variation in natural plant populations in the context of pollinator interactions. We found that evidence for significant pollinator-mediated selection is surprisingly limited among existing studies. We propose several possible explanations related to the complexity in the interaction between the colors of flowers and the sensory and cognitive abilities of pollinators as well as pollinator behavioral responses, on the one hand, and the distribution of variation in color phenotypes and fitness, on the other hand. We emphasize currently persisting weaknesses in experimental procedures, and provide some suggestions for how to improve methodology. In conclusion, we encourage future research to bring together plant and animal scientists to jointly forward our understanding of the mechanisms and circumstances of pollinator-mediated selection on flower color.
Alvaro Daniel Pantoja-Benavides, Gabriel Garces-Varon,
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.702892

Abstract:
Rice yield has decreased due to climate variability and change in Colombia. Plant growth regulators have been used as a strategy to mitigate heat stress in different crops. Therefore, this study aimed to evaluate the effect of foliar applications of four growth regulators [auxins (AUX), brassinosteroids (BR), cytokinins (CK), or gibberellins (GA)] on physiological (stomatal conductance, total chlorophyll content, Fv/Fm ratio, plant canopy temperature, and relative water content) and biochemical (Malondialdehyde (MDA) and proline contents) variables in two commercial rice genotypes exposed to combined heat stress (high day and nighttime temperatures). Two separate experiments were carried out using plants of two rice genotypes, Fedearroz 67 (“F67”) and Fedearroz 2000 (“F2000”) for the first and second experiments, respectively. Both trials were analyzed together as a series of experiments. The established treatments were as follows: absolute control (AC) (rice plants grown under optimal temperatures (30/25°C day/nighttime temperatures), heat stress control (SC) [rice plants only exposed to combined heat stress (40/30°C)], and stressed rice plants and sprayed twice (5 days before and after heat stress) with a plant growth regulator (stress+AUX, stress+BR, stress+CK, or stress+GA). The results showed that foliar CK sprays enhanced the total chlorophyll content in both cultivars (3.25 and 3.65 mg g−1 fresh weight for “F67” and “F2000” rice plants, respectively) compared to SC plants (2.36 and 2.56 mg g−1 fresh weight for “F67,” and “F2000” rice plants, respectively). Foliar CK application also improved stomatal conductance mainly in “F2000” rice plants compared to their heat stress control (499.25 vs.150.60 mmol m−2s−1). Foliar BR or CK sprays reduced plant canopy temperature between 2 and 3°C and MDA content in plants under heat stress. The relative tolerance index suggested that foliar CK (97.69%), and BR (60.73%) applications helped to mitigate combined heat stress mainly in “F2000” rice plants. In conclusion, foliar BR or CK applications can be considered an agronomic strategy to help to ameliorate the negative effect of combined heat stress conditions on the physiological behavior of rice plants.
Yiqing Feng, Xin Fu, Lujie Han, Chenxiao Xu, Chaoyue Liu, Huangai Bi, Xizhen Ai
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.686545

Abstract:
Melatonin (MT) and nitric oxide (NO) are two multifunctional signaling molecules that are involved in the response of plants to abiotic stresses. However, how MT and NO synergize in response to cold stress affecting plants is still not clear. In this study, we found that endogenous MT accumulation under cold stress was positively correlated with cold tolerance in different varieties of cucumber seedlings. The data presented here also provide evidence that endogenous NO is involved in the response to cold stress. About 100 μM MT significantly increased the nitrate reductase (NR) activity, NR-relative messenger RNA (mRNA) expression, and endogenous NO accumulation in cucumber seedlings. However, 75 μM sodium nitroprusside (SNP, a NO donor) showed no significant effect on the relative mRNA expression of tryptophan decarboxylase (TDC), tryptamine-5-hydroxylase (T5H), serotonin-N-acetyltransferase (SNAT), or acetylserotonin O-methyltransferase (ASMT), the key genes for MT synthesis and endogenous MT levels. Compared with H2O treatment, both MT and SNP decreased electrolyte leakage (EL), malondialdehyde (MDA), and reactive oxygen species (ROS) accumulation by activating the antioxidant system and consequently mitigated cold damage in cucumber seedlings. MT and SNP also enhanced photosynthetic carbon assimilation, which was mainly attributed to an increase in the activity and mRNA expression of the key enzymes in the Calvin–Benson cycle. Simultaneously, MT- and SNP-induced photoprotection for both photosystem II (PSII) and photosystem I (PSI) in cucumber seedlings, by stimulating the PsbA (D1) protein repair pathway and ferredoxin-mediated NADP+ photoreduction, respectively. Moreover, exogenous MT and SNP markedly upregulated the expression of chilling response genes, such as inducer of CBF expression (ICE1), C-repeat-binding factor (CBF1), and cold-responsive (COR47). MT-induced cold tolerance was suppressed by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO, a specific scavenger of NO). However, p-chlorophenylalanine (p-CPA, a MT synthesis inhibitor) did not affect NO-induced cold tolerance. Thus, novel results suggest that NO acts as a downstream signal in the MT-induced plant tolerance to cold stress.
Saad Serfraz, Vikas Sharma, Florian Maumus, Xavier Aubriot, Andrew D. W. Geering,
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.683681

Abstract:
Endogenous viral elements (EVEs) are widespread in plant genomes. They result from the random integration of viral sequences into host plant genomes by horizontal DNA transfer and have the potential to alter host gene expression. We performed a large-scale search for co-transcripts including caulimovirid and plant sequences in 1,678 plant and 230 algal species and characterized 50 co-transcripts in 45 distinct plant species belonging to lycophytes, ferns, gymnosperms and angiosperms. We found that insertion of badnavirus EVEs along with Ty-1 copia mobile elements occurred into a late blight resistance gene (R1) of brinjal eggplant (Solanum melongena) and wild relatives in genus Solanum and disrupted R1 orthologs. EVEs of two previously unreported badnaviruses were identified in the genome of S. melongena, whereas EVEs from an additional novel badnavirus were identified in the genome of S. aethiopicum, the cultivated scarlet eggplant. Insertion of these viruses in the ancestral lineages of the direct wild relatives of the eggplant would have occurred during the last 3 Myr, further supporting the distinctiveness of the group of the eggplant within the giant genus Solanum.
Xiaomin Xue, Ying Duan, Jinzheng Wang, Fengwang Ma, Pengmin Li
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.694954

Abstract:
Light and low temperatures induce anthocyanin accumulation, but intense sunlight causes photooxidative sunburn. Nonetheless, there have been few studies of anthocyanin synthesis under different sunlight intensities and low nighttime temperatures. Here, low nighttime temperatures followed by low light intensity were associated with greater anthocyanin accumulation and the expression of anthocyanin biosynthesis genes in “Fuji” apple peel. UDP-glucose flavonoid-3-O-glucosyltransferase (UFGT) activity was positively associated with anthocyanin enrichment. Ascorbic acid can be used as an electron donor of APX to scavenge H2O2 in plants, which makes it play an important role in oxidative defense. Exogenous ascorbate altered the anthocyanin accumulation and reduced the occurrence of high light–induced photooxidative sunburn by removing hydrogen peroxide from the peel. Overall, low light intensity was beneficial for the accumulation of anthocyanin and did not cause photooxidative sunburn, whereas natural light had the opposite effect on the apple peel at low nighttime temperatures. This study provides an insight into the mechanisms by which low temperatures induce apple coloration and high light intensity causes photooxidative sunburn.
Daniel Matsusaka, Daniele Filiault, Diego H. Sanchez,
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.677728

Abstract:
Arabidopsis thaliana shows a wide range of genetic and trait variation among wild accessions. Because of its unparalleled biological and genomic resources, Arabidopsis has a high potential for the identification of genes underlying ecologically important complex traits, thus providing new insights on genome evolution. Previous research suggested that distinct light responses were crucial for Arabidopsis establishment in a peculiar ecological niche of southern Patagonia. The aim of this study was to explore the genetic basis of contrasting light-associated physiological traits that may have mediated the rapid adaptation to this new environment. From a biparental cross between the photomorphogenic contrasting accessions Patagonia (Pat) and Columbia (Col-0), we generated a novel recombinant inbred line (RIL) population, which was entirely next-generation sequenced to achieve ultra-high-density saturating molecular markers resulting in supreme mapping sensitivity. We validated the quality of the RIL population by quantitative trait loci (QTL) mapping for seedling de-etiolation, finding seven QTLs for hypocotyl length in the dark and continuous blue light (Bc), continuous red light (Rc), and continuous far-red light (FRc). The most relevant QTLs, Rc1 and Bc1, were mapped close together to chromosome V; the former for Rc and Rc/dark, and the latter for Bc, FRc, and dark treatments. The additive effects of both QTLs were confirmed by independent heterogeneous inbred families (HIFs), and we explored TZP and ABA1 as potential candidate genes for Rc1 and Bc1QTLs, respectively. We conclude that the Pat × Col-0 RIL population is a valuable novel genetic resource to explore other adaptive traits in Arabidopsis.
Jiangtao Yu, Chanjuan Mao, Qun Zhong, Xuefeng Yao, Peng Li, Chunming Liu,
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.699303

Abstract:
The germination of seeds and establishment of seedling are the preconditions of plant growth and are antagonistically regulated by multiple phytohormones, e.g., ethylene, abscisic acid (ABA), and gibberellic acid (GA). However, the interactions between these phytohormones and their upstream transcriptional regulation during the seed and seedling growth in rice remain poorly understood. Here, we demonstrated a rice NAC (NAM-ATAF-CUC) transcription factor, OsNAC2, the overexpression of which increases the ethylene sensitivity in rice roots during the seedling period. Further study proved that OsNAC2 directly activates the expressions of OsACO and OsACO3, enhancing ethylene synthesis, and then retards seedling establishment. Moreover, OsNAC2 delays the germination of seeds and coleoptile growth through the ABA pathway instead of the ethylene and GA pathway, by targeting the promoters of OsNCED3, OsZEP1, and OsABA8ox1. We also found that OsNAC2 regulates downstream targets in a time-dependent manner by binding to the promoter of OsKO2 in the seedling period but not in the germination stage. Our finding enriched the regulatory network of ethylene, ABA, and GA in the germination of rice seeds and seedling growth, and uncovered new insights into the difference of transcription factors in targeting their downstream components.
, Navin C. Gahtyari, Chandan Roy, Krishna K. Roy, Xinyao He, B. Tembo, Kaijie Xu, Philomin Juliana, Kai Sonder, Muhammad R. Kabir, et al.
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.710707

Abstract:
Wheat blast (WB) caused by Magnaporthe oryzae pathotype Triticum (MoT) is an important fungal disease in tropical and subtropical wheat production regions. The disease was initially identified in Brazil in 1985, and it subsequently spread to some major wheat-producing areas of the country as well as several South American countries such as Bolivia, Paraguay, and Argentina. In recent years, WB has been introduced to Bangladesh and Zambia via international wheat trade, threatening wheat production in South Asia and Southern Africa with the possible further spreading in these two continents. Resistance source is mostly limited to 2NS carriers, which are being eroded by newly emerged MoT isolates, demonstrating an urgent need for identification and utilization of non-2NS resistance sources. Fungicides are also being heavily relied on to manage WB that resulted in increasing fungal resistance, which should be addressed by utilization of new fungicides or rotating different fungicides. Additionally, quarantine measures, cultural practices, non-fungicidal chemical treatment, disease forecasting, biocontrol etc., are also effective components of integrated WB management, which could be used in combination with varietal resistance and fungicides to obtain reasonable management of this disease.
Kijong Song, Dae-Woo Lee, Jeongheon Kim, Jaewook Kim, Hwanuk Guim, Keunhwa Kim, ,
Frontiers in Plant Science, Volume 12; doi:10.3389/fpls.2021.628948

Abstract:
Starch granules in the endodermis of plant hypocotyls act as statoliths that promote hypocotyl negative gravitropism—the directional growth of hypocotyls against gravity—in the dark. To identify the molecular components that regulate hypocotyl negative gravitropism, we performed a mutagenesis screen and isolated reduced gravitropic 1 (rgv1) mutants that lack starch granules in their hypocotyl endodermis and show reduced hypocotyl negative gravitropism in the dark. Using whole genome sequencing, we identified three different rgv1 mutants that are allelic to the previously reported early starvation 1 mutant, which is rapidly depleted of starch just before the dawn. ESV1 orthologs are present in starch-producing green organisms, suggesting ESV1 is a functionally conserved protein necessary for the formation of starch granules. Consistent with this, we found that liverwort and rice ESV1 can complement the Arabidopsis ESV1 mutant phenotype for both starch granules and hypocotyl negative gravitropism. To further investigate the function of ESV1 in other plants, we isolated rice ESV1 mutants and found that they show reduced levels of starch in their leaves and loosely packed starch granules in their grains. Both Arabidopsis and rice ESV1 mutants also lack starch granules in root columella and show reduced root gravitropism. Together, these results indicate ESV1 is a functionally conserved protein that promotes gravitropic responses in plants via its role in starch granule formation.
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