Browsing by Author "Yadukrishnan, Premachandran"

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The B-box bridge between light and hormones in plants
(Elsevier, 2019-02) Yadukrishnan, Premachandran
Plant development is meticulously modulated by interactions between the surrounding environment and the endogenous phytohormones. Light, as an external signal coordinates with the extensive networks of hormones inside the plant to execute its effects on growth and development. Several proteins in plants have been identified for their crucial roles in mediating light regulated development. Among these are the B-box (BBX) family of transcription factors characterized by the presence of zinc-finger B-box domain in their N-terminal region. In Arabidopsis there are 32 BBX proteins that are divided into five structural groups on the basis of the domains present. Several BBX proteins play important roles in seedling photomorphogenesis, neighbourhood detection and photoperiodic regulation of flowering. There is increasing evidence that besides light signaling BBX proteins also play integral roles in several hormone signaling pathways in plants. Here we attempt to comprehensively integrate the roles of multiple BBX proteins in various light and hormone signaling pathways. We further discuss the role of the BBX proteins in mediating crosstalk between the two signaling pathways to harmonize plant growth and development. Finally, we try to analyse the conservation of BBX genes across species and discuss the role of BBX proteins in regulating economically important traits in crop plants.
The B-box protein BBX13/COL15 suppresses photoperiodic flowering by attenuating the action of CONSTANS in Arabidopsis
(Wiley, 2024-08) Yadukrishnan, Premachandran
The optimal timing of transition from vegetative to floral reproductive phase is critical for plant productivity and agricultural yields. Light plays a decisive role in regulating this transition. The B-box (BBX) family of transcription factors regulates several light-mediated developmental processes in plants, including flowering. Here, we identify a previously uncharacterized group II BBX family member, BBX13/COL15, as a negative regulator of flowering under long-day conditions. BBX13 is primarily expressed in the leaf vasculature, buds, and flowers, showing a similar spatial expression pattern to the major flowering time regulators CO and FT. bbx13 mutants flower early, while BBX13-overexpressors exhibit delayed flowering under long days. Genetic analyses showed that BBX13 acts upstream to CO and FT and negatively regulates their expression. BBX13 physically interacts with CO and inhibits the CO-mediated transcriptional activation of FT. In addition, BBX13 directly binds to the CORE2 motif on the FT promoter, where CO also binds. Chromatin immunoprecipitation data indicates that BBX13 reduces the in vivo binding of CO on the FT promoter. Through luciferase assay, we found that BBX13 inhibits the CO-mediated transcriptional activation of FT. Together, these findings suggest that BBX13/COL15 represses flowering in Arabidopsis by attenuating the binding of CO on the FT promoter.
The B-box-containing microprotein miP1a/BBX31 regulates photomorphogenesis and UV-B protection
(OUP, 2019-04) Yadukrishnan, Premachandran
The bZIP transcription factor ELONGATED HYPOCOTYL5 (HY5) represents a major hub in the light-signaling cascade both under visible and UV-B light. The mode of transcriptional regulation of HY5, especially under UV-B light, is not well characterized. B-BOX (BBX) transcription factors regulate HY5 transcription and also posttranscriptionally modulate HY5 to control photomorphogenesis under white light. Here, we identify BBX31 as a key signaling intermediate in visible and UV-B light signal transduction in Arabidopsis (Arabidopsis thaliana). BBX31 expression is induced by UV-B radiation in a fluence-dependent manner. HY5 directly binds to the promoter of BBX31 and regulates its transcript levels. Loss- and gain-of-function mutants of BBX31 indicate that it acts as a negative regulator of photomorphogenesis under white light but is a positive regulator of UV-B signaling. Genetic interaction studies suggest that BBX31 regulates photomorphogenesis independent of HY5. We found no evidence for a direct BBX31-HY5 interaction, and they primarily regulate different sets of genes in white light. Under high doses of UV-B radiation, BBX31 promotes the accumulation of UV-protective flavonoids and phenolic compounds. It enhances tolerance to UV-B radiation by regulating genes involved in photoprotection and DNA repair in a HY5-dependent manner. Under UV-B radiation, overexpression of BBX31 enhances HY5 transcriptional levels in a UV RESISTANCE LOCUS8-dependent manner, suggesting that BBX31 might regulate HY5 transcription.
BBX31 promotes hypocotyl growth, primary root elongation and UV-B tolerance in Arabidopsis
(Taylor & Francis, 2019-03) Yadukrishnan, Premachandran
Photomorphogenesis is an important developmental process that helps the seedlings adapt to external light conditions. B-Box proteins are a family of transcription factors that regulate photomorphogenic responses. BBX31 negatively regulates photomorphogenesis under visible light. In contrast, it promotes photomorphogenesis under UV-B and enhances tolerance to high doses of UV-B radiation. BBX31 and HY5 independently and oppositely regulate the ability of seedlings to adapt to varying light intensities. BBX31 also regulates primary root elongation under low intensities of white light. GC-MS and HPLC-based metabolite profiling identified differential accumulation of multiple primary and secondary metabolites in 35S:BBX31 that might enhance tolerance to UV-B.
Constitutively photomorphogenic1 promotes ABA-mediated inhibition of post-germination seedling establishment
(Wiley, 2020-05) Yadukrishnan, Premachandran
Under acute stress conditions, precocious seedling development may result in the premature death of young seedlings, before they switch to autotrophic growth. The phytohormone abscisic acid (ABA) inhibits seed germination and post-germination seedling establishment under unfavorable conditions. Various environmental signals interact with the ABA pathway to optimize these early developmental events under stress. Here, we show that light availability critically influences ABA sensitivity during early seedling development. In dark conditions, the ABA-mediated inhibition of post-germination seedling establishment is strongly enhanced. COP1, a central regulator of seedling development in the dark, is necessary for this enhanced post-germination ABA sensitivity in darkness. Despite their slower germination, cop1 seedlings establish faster than wild type in the presence of ABA in both light and dark. PHY and CRY photoreceptors that inhibit COP1 activity in light modulate ABA-mediated inhibition of seedling establishment in light. Genetically, COP1 acts downstream to ABI5, a key transcriptional regulator of ABA signaling, and does not influence the transcriptional and protein levels of ABI5 during the early post-germination stages. COP1 promotes post-germination growth arrest independent of the antagonistic interaction between ABA and cytokinin signaling pathways. COP1 facilitates the binding of ABI5 on its target promoters and the ABA-mediated upregulation of these target genes is reduced in cop1-4. Together, our results suggest that COP1 positively regulates ABA signaling to inhibit post-germination seedling establishment under stress.
A COP1-HY5-ABI5 module regulates ABA-mediated post-germination developmental arrest
(Frontiers Media, 2025-11) Yadukrishnan, Premachandran
Abscisic Acid (ABA) is a key phytohormone that regulates plant development under stress. ABA induces dormancy in seeds during maturation, whereas its levels and activity gradually decrease as germination and seedling growth progress. Under abiotic stress conditions, elevated levels of ABA inhibit seed germination and/or impose post-germination growth arrest. The transcription factor ABSCISIC ACID INSENSITIVE 5 (ABI5) regulates the interplay between ABA and light signaling to modulate this process. The light-regulated transcription factor ELONGATED HYPOCOTYL 5 (HY5) modulates ABA-mediated inhibition of post-germination development. However, the interrelation between HY5 and ABI5 in regulating post-germination development remains poorly understood. Here, using molecular, genetic, and biochemical approaches, we show that ABI5 and HY5 proteins reciprocally influence each other’s accumulation during early plant development. We further find that ABA induces nuclear accumulation of COP1, which correlates with reduced HY5 levels and enhanced ABI5 accumulation under stress conditions. Together, our results support a model in which a double-negative feedback loop between HY5 and ABI5 contributes to ABA-mediated post-germination growth arrest.
Double the action: multimodal action of a CONSTANS-LIKE protein enhances stress tolerance in soybean
(OUP, 2023-02) Yadukrishnan, Premachandran
Climate change has intensified the damage caused to agricultural production by abiotic stress conditions such as drought, salinity, freezing, and flooding. More comprehensive understanding of plant stress tolerance mechanisms is crucial for developing future-proof crop varieties. CONSTANS-LIKE (COL) proteins, belonging to the B-box (BBX) family of transcription factors, are well known for their role in light-regulated developmental responses such as photomorphogenesis and photoperiodic flowering (Yadav et al., 2020). However, the role of these proteins in abiotic and biotic stress responses is poorly understood. In this issue of Plant Physiology, Xu et al. (2022) report that GmCOL1a, a COL/BBX protein that promotes flowering in soybean (Glycine max), also enhances tolerance against drought and salinity stress.
Hormones and light-regulated seedling development
(Springer, 2021-10) Yadukrishnan, Premachandran
Light is one of the most important environmental signals, which has a profound impact on plant growth and development. Once a seed germinates, the proper emergence and establishment of the seedling into an autotrophic organism is extremely crucial for its survival. Various steps in the seedling establishment process are remarkably influenced by external light conditions. These steps include the dark-adapted growth of seedlings to emerge out of the soil cover; the opening and expansion of their embryonic leaves once they hit the light above the ground; the synthesis and accumulation of chloroplasts in the green parts to initiate photosynthesis; the accumulation of photoprotective compounds to safeguard the seedling from stress induced by sudden and excessive light exposure; the bending of the seedlings in response to the direction of light; the adjustment of root architecture in response to the direction and availability of light; and the morphogenic changes they undergo in a crowded population to avoid shade and reach for the sunlight. Plants possess specialized photoreceptors such as the Phytochromes, Cryptochromes, Phototropins and UVR8 to perceive different wavelengths of the light spectra. Downstream to these photoreceptors, central molecular players such as ELONGATED HYPOCOTYL 5 (HY5) and PHYTOCHROME INTERACTING FACTORS (PIFs) together with numerous other regulatory proteins establish a highly sophisticated signaling network. The light signaling network often culminates in the regulation of different phytohormones to induce major developmental changes in the plant. This chapter will discuss the finely regulated interaction between light and hormonal pathways in determining the developmental plasticity of plants during seedling development.
HY5 suppresses, rather than promotes, abscisic acid-mediated inhibition of postgermination seedling development
(OUP, 2020-10) Yadukrishnan, Premachandran
Seed germination and postgermination seedling establishment are crucial early developmental events in angiosperms. Although the demarcations between these two successive events appear to be elusive, they have been defined as distinct developmental processes and identified to involve separate regulatory mechanisms at the molecular level. Seed germination is marked by the protrusion of embryonic root out of the seed coat. Postgermination seedling establishment denotes the developmental window after germination that involves the opening, greening, and expansion of cotyledons or foliar leaves, marking the switch to autotrophic development
Let the sunshine in: Abscisic acid modulates shade avoidance by inducing hyponasty movement in Arabidopsis
(OUP, 2023-01) Yadukrishnan, Premachandran
Shade avoidance is a remarkable example of the plasticity exhibited by plants in response to environmental signals. Shade-avoiding plants need to perform an array of morphogenic adjustments upon the sensing of changes in light quality. Such changes in light are perceived as a decrease in the ratio of red to far-red (R/FR) wavelengths caused, for example, by neighboring plants competing for light
Light and abscisic acid interplay in early seedling development
(Wiley, 2020-09) Yadukrishnan, Premachandran
Abscisic acid (ABA) plays a crucial role in plant development, regulating germination, seedling development and stomatal movements, especially under adverse conditions. Light interacts with the ABA signalling pathway to fine tune these processes. Here, we provide an overview of the recent investigations on ABA–light interplay during early plant development after germination. We discuss the multilayered and reciprocal interactions between ABA signalling components and several light signalling modulators, including photoreceptors, transcription factors and posttranslational modifiers. ABSCISIC ACID INSENSITIVE5 acts as a central convergence point for these interactions during postgermination seedling development. ABA also regulates the adaptation of seedlings to challenging light environments. Furthermore, we enlist the role of ABA–light cross-talk in regulating seedling establishment in crops and highlight open questions for future investigations.
Light signaling and UV-B-mediated plant growth regulation
(Wiley, 2020-04) Yadukrishnan, Premachandran
Light plays an important role in plants’ growth and development throughout their life cycle. Plants alter their morphological features in response to light cues of varying intensity and quality. Dedicated photoreceptors help plants to perceive light signals of different wavelengths. Activated photoreceptors stimulate the downstream signaling cascades that lead to extensive gene expression changes responsible for physiological and developmental responses. Proteins such as ELONGATED HYPOCOTYL5 (HY5) and CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) act as important factors which modulate light-regulated gene expression, especially during seedling development. These factors function as central regulatory intermediates not only in red, far-red, and blue light pathways but also in the UV-B signaling pathway. UV-B radiation makes up only a minor fraction of sunlight, yet it imparts many positive and negative effects on plant growth. Studies on UV-B perception, signaling, and response in plants has considerably surged in recent times. Plants have developed different strategies to use UV-B as a developmental cue as well as to withstand high doses of UV-B radiation. Plants’ responses to UV-B are an integration of its cross-talks with both environmental factors and phytohormones. This review outlines the current developments in light signaling with a major focus on UV-B-mediated plant growth regulation.
Mechanisms of action of nanoparticles in living systems
(IGI Global, 2021) Yadukrishnan, Premachandran
Nanoparticles are being formed continuously in processes like mineralization, natural calamities, and geological recycling of matter and present naturally in the environment. In the recent past, nanoparticles and their applications have become an extensive topic of research. Application of nanomaterials in different industries will surely enhance the chances of discharge of nanoparticles into the environment. So, a number of studies have been performed to explore the mode of action of nanoparticles on living organisms and their surroundings. The most reported modes of action of nanoparticles are antimicrobial activity, ROS-induced cytotoxicity, genotoxicity, plant growth promotion, etc. It has been successfully demonstrated that actions of nanoparticles are governed by their size, shape, dose, and concentration. However, a complete mechanism of action of nanoparticles has not been known. The present chapter focuses on the highlights of the mechanisms behind the mode of action of nanoparticles in plants and microorganisms.
Opposite roles of group IV BBX proteins: Exploring missing links between structural and functional diversity
(Taylor & Francis, 2018-08) Yadukrishnan, Premachandran
BBX proteins are a family of zinc finger transcription factors that are versatile regulators of plant development. The 32 BBX proteins in Arabidopsis are subdivided into five structural groups based on their domain structure. Members of group IV play important and diverse roles in light-regulated development. The N-terminal B-box domains mediate DNA binding and transcriptional regulation. The C-terminal region determines the functional diversity of the structurally similar group IV members as reported in our recent study investigating the basis of functional diversification between BBX21 and BBX24. We also found that multi-layered regulation of HY5 by the BBX proteins leads to a diverse repertoire of developmental effects. Here we provide a comprehensive structure-function analysis of the group IV BBX proteins.
Triggered in distress: a miRNA-controlled switch for drought-induced ABA biosynthesis in rice
(OUP, 2022-06) Yadukrishnan, Premachandran
Abiotic stress conditions such as drought, salinity, and flood challenge agricultural production worldwide by adversely affecting crop growth and yield. Plants inherently possess sophisticated response mechanisms for adjusting their physiology to improve survival under stress conditions. Understanding these mechanisms and enhancing them through breeding and biotechnological means are important steps toward developing crop varieties that can perform well under unpredictable climatic extremities of the future. Abscisic acid (ABA) is a key phytohormone that mediates stress responses in all land plants. Stress conditions induce ABA biosynthesis through a series of steps that occur in plastids and cytosol, and the rate-limiting step in this process is catalyzed by enzymes known as 9-cis-epoxycarotenoid dioxygenases (NCEDs) (Nambara and Marion-Poll, 2005). ABA activates a signaling cascade featuring a set of receptors that function redundantly, type 2C protein phosphatases (PP2Cs) that act as co-receptors, sucrose non-fermenting 1-related protein kinase 2 subfamily proteins (SnRK2s) that channel the signal from cytosol to nucleus, and an array of transcription factors that mediate stress-responsive gene expression (Chen et al., 2020). Since elevated levels of ABA can often impart negative effects on growth, a tight modulation of ABA biosynthesis and signaling is necessary to balance growth and stress responses (Chen et al., 2020). In addition to transcriptional regulation, the levels and activities of ABA signaling components are optimized at the post-transcriptional level by miRNAs and at the protein level through post-translational modifications (Nadarajah and Kumar, 2019; Zhang et al., 2019; Chen et al., 2020). However, the precise mechanisms by which ABA biosynthesis is rapidly induced under stress conditions and turned off immediately when the normal growth conditions are restored remain poorly understood.
Two B-box proteins regulate photomorphogenesis by oppositely modulating HY5 through their diverse C-terminal domains
(OUP, 2018-04) Yadukrishnan, Premachandran
The Arabidopsis (Arabidopsis thaliana) BBX family comprises several positive and negative regulators of photomorphogenesis. BBX24, a member of BBX structural group IV, acts as a negative regulator of photomorphogenesis, whereas another member from the same group, BBX21, is a positive regulator. The molecular basis for the functional diversity shown by these related BBX family members is unknown. Using domain-swap lines, we show that the C-terminal regions of BBX24 and BBX21 specify their function. Because both BBX21 and BBX24 work in close association with HY5, we hypothesized that these proteins differentially regulate the levels or activity of HY5 to fulfill their opposite roles. We show that BBX21 can regulate HY5 post-transcriptionally and the two proteins can coordinate to promote photomorphogenesis. By contrast, BBX24 interferes with the binding of HY5 to the promoter of an anthocyanin biosynthetic gene, possibly by heterodimerizing with HY5 and preventing it from binding DNA. Our finding that both BBX21 and BBX24 regulate HY5 activity post-transcriptionally, in opposite ways, suggests that closely related B-box proteins execute contrasting functions through differential regulation of HY5.
Two in one: Splice isoforms of a HY5-homolog in rice regulate plant height in light and darkness
(OUP, 2023-07) Yadukrishnan, Premachandran
Plants possess intricate mechanisms to adjust their growth and development in response to the changes in the quality and quantity of environmental light. Specialized photoreceptors perceive discrete wavelengths of light and transduce the signals to the nucleus, causing widespread changes in the gene expression mediated by an array of transcription factors (Yadav et al. 2020). Seedlings growing in light form short hypocotyls and open and expanded cotyledons (photomorphogenesis), whereas in darkness they form elongated hypocotyls with an apical hook and closed cotyledons