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Cold stress influences the growth and geographical distribution of plants. Tobacco (Nicotiana tabacum L.), a model in plant biology studies and a world-widely cultivated economic plant from tropical America, exhibits extreme sensitivity to low temperatures. The conserved B-BOX (BBX) transcription factors play vital roles in plant photomorphogenesis and flowering regulation, and their functions in abiotic stresses, including cold stress, have been uncovered recently. However, few studies on tobacco BBX genes have been conducted to date. In this study, 49 non-redundant BBX genes have been identified in the reference tobacco genome. Gene structure, phylogenetic relationship, prediction of cis -regulatory elements in promoters, tissue-specific expression patterns, and response to cold stress were conducted on these BBX gene members. The expression of NtBBX9 and NtBBX11 , two close members in the amplified group II, was up-regulated under cold treatments. Overexpression of NtBBX11 embedded the cold tolerance of transgenic plants, while the NtBBX9 overexpressors were susceptible to cold. The NtBBX9 functions as a negative regulator of tobacco response to cold stress, which was confirmed by the phenotype of NtBBX9 RNA-silenced lines. Furthermore, we demonstrated that NtBBX9 and NtBBX11 regulated the cold stress response by alternating the expression of critical cold-regulated genes such as CBFs , LEA14 , and LTI65 and reactive oxygen species (ROS) production. The combination of NtBBX9 and NtBBX11 could facilitate tobacco's rapid response to and recovery from transient cold stress and regulate plant cold-responsive growth in tropical regions. • 49 tobacco NtBBX genes were identified, along with their bioinformatics analysis and potential roles in cold stress. • Overexpression of NtBBX11 improved the tolerance of tobacco to low-temperature stress. • NtBBX9 suppresses NtCBFs and negatively regulates cold tolerance in tobacco. [ABSTRACT FROM AUTHOR]

Plant geographical distribution, growth and development, and yield, are to a greater extend affected by the environmental factors, including cold stress. Low-temperature affects enzyme activity, membrane functionality, and cell dehydration, leading to cell metabolic instability or autophagy. Nonetheless, plants have evolved complex biochemical and molecular mechanisms to adapt to cold stress, regulated through transcriptional and translational modifications of genes. These complex mechanisms are principally divided into ABA-dependent and -independent pathways. Abscisic acid (ABA), as a crucial component in the pathways during the cold stress, regulates the expression of Cold-Responsive (COR) genes through several transcription factors such as the bZIP, HOS members, homo box, H4, and Zn finger factors. Particularly, in the ABA-independent pathway, the cold stress is regulated through the C-repeat binding factors (CBF s), and ABA activates the expression of the Inducer of CBF expression 1 (ICE1) through the Mitogen-Activated Protein Kinase (MAPK) signaling pathway. Consequently, upregulating the transcription and expression of CBF genes and COR genes downstream in a chain reaction, through binding to the C-repeat/Dehydration Responsive Element (CRT/DRE). In addition, the transcriptional and post-translational modifications (PTMs) modulate gene expressions in the signaling cascade at various levels of response leading to plant low temperature stress acclimation. This review paper discusses and summarizes the molecular mechanisms governing cold stress responses, addressing current researches and findings in light of the cold stress and their implications on plant genetic improvement. • The ICE-CBF pathway regulates cold adaptation at different levels of response. • SnRK2 regulates the ABA-dependent COR genes to modulate cold stress through interaction between the bZIP and ABREs. • ABA-independent pathway regulates cold stress through the CBF/DREB1. [ABSTRACT FROM AUTHOR]

Red or purple coloration of abaxial (lower) leaf surfaces is a taxonomically-widespread phenomenon that has evolved independently in multiple plant lineages. The trait has long been associated with deeply-shaded forest understory habitats, but also occurs in many taxa adapted to high light, including aquatic plants with floating leaves, and herbs that thrive in sun-exposed meadows, rocks, or cliff faces. We surveyed the literature for information related to the taxonomic and environmental distribution of plants displaying abaxial leaf reddening, the chemical structures and anatomical locations of pigments associated with abaxial leaf reddening (if known), and the physiological and ecological (e.g., defensive– anti-herbivory and anti-pathogenic) hypotheses proposed to explain their occurrence. We report examples of abaxial leaf reddening in more than 50 angiosperm families and 100 genera, as well as analogous coloration in some basal plant lineages (e.g., selaginellins in ventral surfaces of Selaginella microphylls, auronidins in ventral surfaces of liverwort thalli). Leaf-warming was one of the first hypotheses proposed for abaxial leaf reddening (19th century); while slight (1–2 °C) warming effects were reported, few studies have since successfully corroborated these early results. Lee et al. (1979) proposed that abaxial red pigments back-scatter red-photons, maximizing light capture efficiency of the leaf in light-limited environments. This hypothesis was largely refuted by later studies. The photoprotection hypothesis is currently the most well-supported explanation for abaxial leaf reddening, whereby red pigments function to attenuate excess photons either directly incident on the abaxial surface of inclined/inverted leaves, or transmitted through adaxial cell layers. This function is beneficial in understory environments exposed to frequent high-light events (e.g., sunflecks, sungaps), as well as in high light environments or seasons. However, this case is far from "closed", as photoprotective effects have only been shown for a few select species, and many ecological hypotheses (e.g., aposematism, leaf camouflage, undermining insect camouflage, defense from fungi, interference competition) have not been fully tested. • Abaxial leaf reddening evolved many times, occurring in >50 angiosperm families. • Structure (and color) of abaxial red pigments is largely influenced by phylogeny. • Photoprotection is the most well-supported hypothesis for this leaf trait. • Warming and interference competition hypotheses need more experimental support. • Hypotheses not tested fully include aposematism, camouflage, anti-fungal defense. [ABSTRACT FROM AUTHOR]

Nonstructural carbohydrates (NSC) are the crucial components of plant metabolism, and NSC dynamics provide essential information on plant carbon balance, which usually changes toward the distribution limits of plants. NSC have been extensively used to study the elevational limit in trees all around the world. For alpine herbs, which occupy vast areas beyond treelines, such investigations are still lacking. To assess whether carbon supply is a limiting factor for the upper distribution limits of alpine herbs, we studied NSC in belowground organs of 11 perennial species across their 4500–6000 m elevation ranges in the Western Himalayas at the peak of the growing season. We found a general elevational increase in total NSC within and across species. Studied alpine plants contain simple sugars and fructans as the main NSC and less so starch. Species- and compound-specific elevation patterns were found for different NSC compounds, suggesting a regulatory role of NSC in alpine herbs acclimation rather than a general accumulation of all NSC resulting from growth limitation. Similar to studies on treeline NSC dynamics, our study shows that reduced carbon supply is an unlikely cause of high-elevation range limits in herbs. Yet, the elevational NSC dynamics in alpine herbs still needs further exploration, with an emphasis on different compounds and their function in acclimatory metabolic processes, to clearly identify the key mechanisms determining plant range limits. • Nonstructural carbohydrates (NSC) shortage is not a cause of plant elevation limits • Total NSC in studied Himalayan plants generally increased with elevation. • Simple sugars and fructans predominate in plant belowground organs. • Individual types of NSC compounds suggest an active acclimation to elevation [ABSTRACT FROM AUTHOR]

Plants being sessile are constantly challenged by numerous abiotic stressors that jeopardize their survival. Drought stress is a major constraint in sustainable agriculture that affects plant distribution, growth, and productivity. Plants use multidimensional adaptation tactics at cellular, molecular, and biochemical levels to combat drought stress. These adaptive strategies have been extensively studied, and a variety of drought-resistance genes have recently been discovered. However, translating this information from the laboratory to field conditions is still a major challenge. Hence, developing novel long-term and successful drought mitigation strategies is an important aim in agriculture, as it is critical to ensure food security. One such approach is to explore the plant microbiome, which has recently become a research frontier. Plant microbiome engineering is being examined as a new aspect of sustainable agriculture, with the potential to improve crop resilience to drought. Plants restructure their microbiome against drought stress by employing the "cry for help" strategy, which can both alleviate stress and can improve health and nutrition availability. Mechanistic insights into the complex feedback between microbes and plants during and after water stress are required to fully harness the potential of above- and below-ground microbiome. The use of high-throughput tools to investigate the ecological, biochemical, physiological, and molecular aspects of the plant microbiome under drought stress will improve our ability to improve the drought resilience of crops in the future. This review highlights recent findings on the impact of drought and related signaling in plants. We also discuss the function of the plant microbiome in drought resistance in plants, as well as possible future research directions. Furthermore, we discuss the roles of multiomics, synthetic microbial communities (SynComs,) and host-mediated microbiome engineering for developing drought-resilient microbial communities in sustainable agriculture. Finally, we assess the challenges encountered and make recommendations for future endeavors to extend plant microbiome applications from the lab to the field. • Drought negatively impacts sustainable agriculture. • Plants "cry for help" during drought and restructure their microbiome. • Harnessing the plant microbiome may ameliorate the effect of drought. • Drought stress management should involve microbiome engineering. • Plant microbiome applications need to be translated from lab to field. [ABSTRACT FROM AUTHOR]

Low temperature stress limits the geographical distribution of tea plants (Camellia sinensis) and the yield and quality of tea. CsICE1 is a crucial regulator of tea plant's cold signaling pathway; however, the regulatory mechanism of CsICE1 is still unclear. In this study, we found that the N-terminus of CsICE1 contains a transcriptional activation domain and a region of protein interaction. Yeast two-hybrid and bimolecular fluorescence complementation experiments confirmed that CsWRKY4 and CsOCP3 interacted with CsICE1 in the nucleus. Like CsICE1, CsWRKY4 and CsOCP3 were localized in the nucleus, and CsOCP3 was also targeted to the chloroplast. The expression of CsWRKY4 and CsOCP3 was downregulated under cold stress, unlike that of CsICE1. Under biotic stresses and salicylic acid treatment, the expression of all three genes was increased, whereas jasmonic acid treatment resulted in decreased expression of all three genes. Dual-luciferase transient assays revealed that CsICE1 promoted the expression of CsCBF1 and CsCBF3 , whereas CsWRKY4 and CsOCP3 inhibited the expression of CsCBF1 and CsCBF3 and attenuated their induction by CsICE1. Taken together, these results suggest that CsWRKY4 and CsOCP3 interact with CsICE1 and regulate CsCBF1/3 , thus mediating the stress response in tea plant. Furthermore, these results highlight that CsICE1 is not only a key component in the low temperature signal response pathway, but it may also serve as a point of confluence for cold and other signaling pathways. • CsCBF1 and CsCBF3 are target genes of CsICE1. • CsICE1 N-terminus contains a transcriptional activation domain. • CsWRKY4 and CsOCP3 interact with CsICE1 and regulate CsCBF1/3. • CsICE1 is a convergence point integrating cold and other signaling pathways. [ABSTRACT FROM AUTHOR]