Overexpression of BBX18 Promotes Thermomorphogenesis Through the PRR5-PIF4 Pathway

Thermomorphogenesis is the morphological response of plants to an elevation in the ambient temperature, which is mediated by the bHLH transcription factor PIF4. The evening-expressed clock component, PRR5, directly represses the expression of PIF4 mRNA. Additionally, PRR5 interacts with PIF4 protein and represses its transactivation activity, which in turn suppresses the thermoresponsive growth in the evening. Here, we found that the B-box zinc finger protein, BBX18, interacts with PRR5 through the B-Box2 domain. Deletion of the B-Box2 domain abolished the functions of BBX18, including the stimulation of PIF4 mRNA expression and hypocotyl growth. Overexpression of BBX18, and not of B-Box2-deleted BBX18, restored the expression of thermoresponsive genes in the evening. We further show that BBX18 prevents PRR5 from inhibiting PIF4-mediated high temperature responses. Taken together, our results suggest that BBX18 regulates thermoresponsive growth through the PRR5-PIF4 pathway.

BBX proteins promote HY5-mediated UVR8 signaling in Arabidopsis

Plants undergo photomorphogenic development in the presence of light. Photomorphogenesis is repressed by the E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1), which binds substrates through their valine-proline (VP) motifs. The UV RESISTANCE LOCUS8 (UVR8) photoreceptor senses UV-B and inhibits COP1 through cooperative binding of its own VP motif mimicry and its photosensing core to COP1, thereby preventing COP1 binding to substrates, including the bZIP transcriptional regulator ELONGATED HYPOCOTYL5 (HY5). As a key promoter of visible light and UV-B photomorphogenesis, HY5 functions together with the B-box family transcription factors BBX20-22 that were recently described as HY5 rate-limiting coactivators under red light. Here we describe a hypermorphic bbx21-3D mutant with enhanced photomorphogenesis, which carries a proline-314 to leucine mutation in the VP motif that impairs interaction with and regulation through COP1. We show that BBX21 and BBX22 are UVR8-dependently stabilized after UV-B exposure, which is counteracted by a repressor induced by HY5/BBX activity. bbx20 bbx21 bbx22 mutants under UV-B are impaired in hypocotyl growth inhibition, photoprotective pigment accumulation, and expression of several HY5-dependent genes. We conclude that BBX20-22 importantly contribute to HY5 activity in a subset of UV-B responses, but that additional, presently unknown coactivators for HY5 are functional in early UVR8 signaling.

Seed Germination and Seedling Growth Responses to Different Sources and Application Rates of Hydrothermal Carbonization Processed Liquid

Hydrothermal carbonization processed liquid (HTCPL) is a by-product of hydrothermal carbonization of biomass, which is used sparingly as natural fertilizer. A study was performed in the Faculty of Agriculture, Dalhousie University (Canada) between June 2019 and April 2020 to evaluate the elemental composition of HTCPL derived from three different biomass feedstock; namely, seafood compost; buckwheat (Fagopyrum esculentum), and willow (Salix babylonica). Different HTCPL application rates (0-10%) were tested on seed germination and seedling growth of pea (Pisum sativum), sunflower (Helianthus annuus), pac choi (Brassica rapa subsp. chinensis), kale (Brassica oleracea var. sabellica) and lettuce (Lactuca sativa). Elemental composition was higher in the HTCPLs compared to their respective feedstocks except for nitrogen. The 5% and 10% willow HTCPL with a pH between 3.8-4.0 inhibited seed germination and seedling growth compared to the other treatments with a pH range between 4.6-5.8. Kale, lettuce and sunflower radicle and hypocotyl growth were promoted following treatments of their respective seeds with seafood compost HTCPL while pea radicle and hypocotyl lengths were best promoted by 5% buckwheat and 10% seafood compost HTCPLs. Comparatively, 0.5% willow HTCPL increased surface area of seedling radicles while 1% willow and 0.5% buckwheat HTCPLs increased surface area of hypocotyls, irrespective of plant species. The distinction among the treatments was demonstrated on a 2-dimensional principal component analysis biplot that explained 89% of the variations in dataset. Overall, buckwheat HTCPL proved to be more effective at increasing seed germination and seedling growth compared to the other HTCPLs. The inhibitory effect of willow HTCPL at high application rate (5-10%) were obvious for all plant species. A comprehensive non-targeted chemical profile of HTCPL will help to explain mechanisms.

Transcriptome and Metabolome Comparison of Smooth and Rough Citrus limon L. Peels Grown on Same Trees and Harvested in Different Seasons

Background: Farmers harvest two batches fruits of Lemons (Citrus limon L. Burm. f.) i.e., spring flowering fruit and autumn flowering fruit in dry-hot valley in Yunnan, China. Regular lemons harvested in autumn have smooth skin. However, lemons harvested in spring have rough skin, which makes them less attractive to customers. Furthermore, the rough skin causes a reduction in commodity value and economical losses to farmers. This is a preliminary study that investigates the key transcriptomic and metabolomic differences in peels of lemon fruits (variety Yuning no. 1) harvested 30, 60, 90, 120, and 150 days after flowering from the same trees in different seasons.Results: We identified 5,792, 4,001, 3,148, and 5,287 differentially expressed genes (DEGs) between smooth peel (C) and rough peel (D) 60, 90, 120, and 150 days after flowering, respectively. A total of 1,193 metabolites differentially accumulated (DAM) between D and C. The DEGs and DAMs were enriched in the mitogen-activated protein kinase (MAPK) and plant hormone signaling, terpenoid biosynthesis, flavonoid, and phenylalanine biosynthesis, and ribosome pathways. Predominantly, in the early stages, phytohormonal regulation and signaling were the main driving force for changes in peel surface. Changes in the expression of genes associated with asymmetric cell division were also an important observation. The biosynthesis of terpenoids was possibly reduced in rough peels, while the exclusive expression of cell wall synthesis-related genes could be a possible reason for the thick peel of the rough-skinned lemons. Additionally, cell division, cell number, hypocotyl growth, accumulation of fatty acids, lignans and coumarins- related gene expression, and metabolite accumulation changes were major observations.Conclusion: The rough peels fruit (autumn flowering fruit) and smooth peels fruit (spring flowering fruit) matured on the same trees are possibly due to the differential regulation of asymmetric cell division, cell number regulation, and randomization of hypocotyl growth related genes and the accumulation of terpenoids, flavonoids, fatty acids, lignans, and coumarins. The preliminary results of this study are important for increasing the understanding of peel roughness in lemon and other citrus species.

Use of organic biostimulant for growing Siberian spruce seedlings

This study aims to assess the possibility of using a biostimulant Verva-spruce based on spruce’s natural phenolic compounds to reduce the time of growing planting material with improved features. The targets were seeds and 1-4-year-old seedlings of Siberian spruce, untreated and treated with the biostimulant. The effect of the biostimulant on seed germination, seedlings growth, and the pigment’s content in needles were studied. Results shown that soaking seeds in biostimulant at a concentration of 0.00025% increased the germination energy and accelerated hypocotyl growth. Moreover, using the biostimulant significantly increased the growth rate of experimental seedlings and heightened the amount of green pigment chlorophyll a up to 2.5 times. In 2020, in order to study the dynamics of the qualitative characteristics of the plants grown using biostimulant, experimental forest plantations of 4-year-old Siberian spruce seedlings were planted in the Altai-Sayan mountain taiga area. The experimental plantation will be monitored at least until the closure of the canopy.

ATANN3 is involved in extracellular ATP-regulated auxin transport and distribution in Arabidopsis thaliana seedlings

Background Extracellular ATP (eATP) exists in the apoplast of plants and plays multiple roles in growth, development, and stress responses. It has been reported that eATP stimulation suppresses growth rate and alters growth orientation of root and hypocotyls of Arabidopsis thaliana seedlings by affecting auxin accumulation and transport in these organs. However, the mechanism of eATP-stimulated vegetative organ growth remains unclear. Annexins are involved in multiple aspects of plant cellular metabolism, while the role of annexins in response to apoplast signal remains unclear. Here, by using loss-of-function mutants, we investigated the role of several annexins in eATP-regulated root and hypocotyl growth. Since mutant of AtANN3 did not respond to eATP sensitively, the role of AtANN3 in eATP regulated auxin transport was intensively investigated. Results First, the inhibitory effect of eATP on root or hypocotyl elongation was weakened or impaired in AtANN3 null mutants (atann3). Meanwhile, single-, double- or triple-null mutant of AtANN1, AtANN2 or AtANN4 responded to eATP stimulation in same manner and degree with Col-0. The abundance and distribution of Dr5-GUS and Dr5-GFP indicated that eATP-induced accumulation and asymmetric distribution of auxin in root tip or hypocotyl cells, which appeared in wild type controls, were lacking in atann3 seedlings. Further, eATP-induced accumulation and asymmetric distribution of PIN2-GFP in root tip cells or PIN3-GFP in hypocotyl cells were reduced in atann3 seedlings. Conclusions AtANN3 may be involved in eATP-regulated seedling growth through regulating auxin transport and accumulation in vegetative organs.

Out of the Dark and Into the Light: A New View of Phytochrome Photobodies

Light is a critical environmental stimulus for plants, serving as an energy source via photosynthesis and a signal for developmental programming. Plants perceive light through various light-responsive proteins, termed photoreceptors. Phytochromes are red-light photoreceptors that are highly conserved across kingdoms. In the model plant Arabidopsis thaliana, phytochrome B serves as a light and thermal sensor, mediating physiological processes such as seedling germination and establishment, hypocotyl growth, chlorophyll biogenesis, and flowering. In response to red light, phytochromes convert to a biologically active form, translocating from the cytoplasm into the nucleus and further compartmentalizes into subnuclear compartments termed photobodies. PhyB photobodies regulate phytochrome-mediated signaling and physiological outputs. However, photobody function, composition, and biogenesis remain undefined since their discovery. Based on photobody cellular dynamics and the properties of internal components, photobodies have been suggested to undergo liquid-liquid phase separation, a process by which some membraneless compartments form. Here, we explore photobodies as environmental sensors, examine the role of their protein constituents, and outline the biophysical perspective that photobodies may be undergoing liquid-liquid phase separation. Understanding the molecular, cellular, and biophysical processes that shape how plants perceive light will help in engineering improved sunlight capture and fitness of important crops.

Xyloglucan Remodeling Defines Auxin-Dependent Differential Tissue Expansion in Plants

Size control is a fundamental question in biology, showing incremental complexity in plants, whose cells possess a rigid cell wall. The phytohormone auxin is a vital growth regulator with central importance for differential growth control. Our results indicate that auxin-reliant growth programs affect the molecular complexity of xyloglucans, the major type of cell wall hemicellulose in eudicots. Auxin-dependent induction and repression of growth coincide with reduced and enhanced molecular complexity of xyloglucans, respectively. In agreement with a proposed function in growth control, genetic interference with xyloglucan side decorations distinctly modulates auxin-dependent differential growth rates. Our work proposes that auxin-dependent growth programs have a spatially defined effect on xyloglucan’s molecular structure, which in turn affects cell wall mechanics and specifies differential, gravitropic hypocotyl growth.