The ubiquitin‐proteasome system (UPS) is a rapid regulatory mechanism for selective protein degradation in plants and plays crucial roles in growth and development. There is increasing evidence that ...the UPS is also an integral part of plant adaptation to environmental stress, such as drought, salinity, cold, nutrient deprivation and pathogens. This review focuses on recent studies illustrating the important functions of the UPS components E2s, E3s and subunits of the proteasome and describes the regulation of proteasome activity during plant responses to environment stimuli. The future research hotspots and the potential for utilization of the UPS to improve plant tolerance to stress are discussed.
The ubiquitin‐proteasome system (UPS) plays crucial roles in plant responses to environment stimuli through degrading distinct target proteins. This review summaries recent progress in our understanding of the regulation of UPS components, subunits and proteasome activity under abiotic and biotic stress, and future research hotspots are discussed.
Phospholipids, including phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylserine (PS) and phosphoinositides, have emerged as an ...important class of cellular messenger molecules in various cellular and physiological processes, of which PA attracts much attention of researchers. In addition to its effect on stimulating vesicle trafficking, many studies have demonstrated that PA plays a crucial role in various signaling pathways by binding target proteins and regulating their activity and subcellular localization. Here, we summarize the functional mechanisms and target proteins underlying PA‐mediated regulation of cellular signaling, development, hormonal responses, and stress responses in plants.
Phosphatidic acid has emerged as an important cellular messenger in various cellular and physiological processes, which functions by binding target proteins and regulating their activities and subcellular localizations. In this review, we summarize the functional mechanisms underlying PA‐mediated regulation of cellular signaling, development, hormonal responses, and stress responses in plants.
Starch biosynthesis is important for plant development and is a critical factor in crop quality and nutrition. As a complex metabolic pathway, the regulation of starch biosynthesis is still poorly ...understood. We here present the identification of candidate regulators for starch biosynthesis by gene coexpression analysis in rice (Oryza sativa). Starch synthesis genes can be grouped into type I (in seeds; sink tissues) and type II (in vegetative tissues; source tissues), and 307 and 621 coexpressed genes are putatively involved in the regulation of starch biosynthesis in rice seeds and vegetative tissues, respectively. Among these genes, Rice Starch Regulator1 (RSR1), an APETALA2/ethylene-responsive element binding protein family transcription factor, was found to negatively regulate the expression of type I starch synthesis genes, and RSR1 deficiency results in the enhanced expression of starch synthesis genes in seeds. Seeds of the knockout mutant rsr1 consistently show the increased amylose content and altered fine structure of amylopectin and consequently form the round and loosely packed starch granules, resulting in decreased gelatinization temperature. In addition, rsr1 mutants have a larger seed size and increased seed mass and yield. In contrast, RSR1 overexpression suppresses the expression of starch synthesis genes, resulting in altered amylopectin structure and increased gelatinization temperature. Interestingly, a decreased proportion of A chains in rsr1 results in abnormal starch granules but reduced gelatinization temperature, whereas an increased proportion of A chains in RSR1-overexpressing plants leads to higher gelatinization temperatures, which is novel and different from previous reports, further indicating the complicated regulation of starch synthesis and determination of the physicochemical properties of starch. These results demonstrate the potential of coexpression analysis for studying rice starch biosynthesis and the regulation of a complex metabolic pathway and provide informative clues, including the characterization of RSR1, to facilitate the improvement of rice quality and nutrition.
Grain size is a major determinant of cereal grain yields; however, the relevant regulatory mechanisms controlling this trait have not been fully elucidated. The rice (Oryza sativa) mutant short ...grain6 (sg6) was identified based on its reduced grain length and weight. Here, we functionally characterized the role of SG6 in determining grain size through the regulation of spikelet hull cell division. SG6 encodes a previously uncharacterized plant AT‐rich sequence and zinc‐binding (PLATZ) protein that is ubiquitously localized throughout the cell and is preferentially expressed in the early developing panicles but not in the endosperm. The overexpression of SG6 resulted in significantly larger and heavier grains, as well as increased plant heights, which is consistent with its elevated spikelet hull cell division rate. Yeast two‐hybrid analyses revealed that SG6 interacts with the core cell cycle machinery DP protein and several other putative cell division regulators, consistent with our transcriptomic analysis, which showed that SG6 activates the expression of many DNA replication and cell‐cycle‐related genes. These results confirm the crucial role of SG6 in determining grain size by regulating spikelet hull cell division and provide clues for understanding the functions of PLATZ family proteins and the network regulating cereal grain size.
We functionally characterized rice Short Grain 6 (SG6), a previously uncharacterized plant AT‐rich sequence and zinc‐binding protein, in determining the grain size by regulating spikelet hull cell division. Our work provided the informative clues for understanding the functions of PLATZ family proteins and the molecular network regulating cereal grain size.
The plant hormone gibberellin (GA) is crucial for multiple aspects of plant growth and development. To study the relevant regulatory mechanisms, we isolated a rice mutant earlier flowering1, el1, ...which is deficient in a casein kinase I that has critical roles in both plants and animals. el1 had an enhanced GA response, consistent with the suppression of EL1 expression by exogenous GA3. Biochemical characterization showed that EL1 specifically phosphorylates the rice DELLA protein SLR1, proving a direct evidence for SLR1 phosphorylation. Overexpression of SLR1 in wild‐type plants caused a severe dwarf phenotype, which was significantly suppressed by EL1 deficiency, indicating the negative effect of SLR1 on GA signalling requires the EL1 function. Further studies showed that the phosphorylation of SLR1 is important for maintaining its activity and stability, and mutation of the candidate phosphorylation site of SLR1 results in the altered GA signalling. This study shows EL1 a novel and key regulator of the GA response and provided important clues on casein kinase I activities in GA signalling and plant development.
Summary
The drought caused by global warming seriously affects the crop growth and agricultural production. Plants have evolved distinct strategies to cope with the drought environment. Under drought ...stress, energy and resources should be diverted from growth toward stress management.
However, the molecular mechanism underlying coordination of growth and drought response remains largely elusive.
Here, we discovered that most of the gibberellin (GA) metabolic genes were regulated by water scarcity in rice, leading to the lower GA contents and hence inhibited plant growth. Low GA contents resulted in the accumulation of more GA signaling negative regulator SLENDER RICE 1, which inhibited the degradation of abscisic acid (ABA) receptor PYL10 by competitively binding to the co‐activator of anaphase‐promoting complex TAD1, resulting in the enhanced ABA response and drought tolerance.
These results elucidate the synergistic regulation of crop growth inhibition and promotion of drought tolerance and survival, and provide useful genetic resource in breeding improvement of crop drought resistance.
Leaf senescence is a complex process regulated by developmental and environmental factors, and plays a pivotal role in the development and life cycle of higher plants. Casein kinase 1 (CK1) is a ...highly conserved serine/threonine protein kinase in eukaryotes and functions in various cellular processes including cell proliferation, light signaling and hormone effects of plants. However, the biological function of CK1 in plant senescence remains unclear. Through systemic genetic and biochemical studies, we here characterized the function of Arabidopsis EL1-like (AEL), a CK1, in promoting leaf senescence by stimulating ethylene biosynthesis through phosphorylating transcription factor WRKY22. Seedlings lacking or overexpressing AELs presented delayed or accelerated leaf senescence, respectively. AELs interact with and phosphorylate WRKY22 at Thr57, Thr60 and Ser69 residues to enhance whose transactivation activity. Being consistent, increased or suppressed phosphorylation of WRKY22 resulted in the promoted or delayed leaf senescence. WRKY22 directly binds to promoter region and stimulates the transcription of 1-amino-cyclopropane-1-carboxylate synthase 7 gene to promote ethylene level and hence leaf senescence. Our studies demonstrated the crucial role of AEL-mediated phosphorylation in regulating ethylene biosynthesis and promoting leaf senescence by enhancing WRKY22 transactivation activity, which helps to elucidate the fine-controlled ethylene biosynthesis and regulatory network of leaf senescence.
Rice leaf inclination is an important agronomic trait, closely related to plant architecture and yield. Identification of genes controlling leaf inclination would assist in crop improvement. Although ...various factors, including the plant hormones auxin and brassinosteroids, have been shown to regulate lamina joint development, the role of microRNAs in regulating leaf inclination remains largely unknown. Here, we functionally characterize the role of rice miR394 and its target, LEAF INCLINCATION 4 (LC4), which encodes an F‐box protein, in the regulation of leaf inclination. We show that miR394 and LC4 work, antagonistically, to regulate leaf lamina joint development and rice architecture, by modulating expansion and elongation of adaxial parenchyma cells. Suppressed expression of miR394, or enhanced expression of LC4, results in enlarged leaf angles, whereas reducing LC4 expression by CRISPR/Cas9 leads to reduced leaf inclination, suggesting LC4 as candidate for use in rice architecture improvement. LC4 interacts with SKP1, a component of the SCF E3 ubiquitin ligase complex, and transcription of both miR394 and LC4 are regulated by auxin. Rice plants with altered expression of miR394 or LC4 have altered auxin responses, indicating that the miR394‐LC4 module mediates auxin effects important for determining rice leaf inclination and architecture.
As an important agronomic trait, leaf inclination closely relates to plant architecture and yield. Here we showed that rice microRNA (miR394) is regulated by auxin and functions antagonistically with F‐box protein LEAF INCLINATION 4 (LC4) to regulate leaf lamina joint development, and LC4 is a candidate for breeding rice with the ideal architecture.
Plant architecture plays a major role in canopy photosynthesis and biomass production, and plants adjust their growth (and thus architecture) in response to changing environments. Leaf angle is one ...of the most important traits in rice (Oryza sativa L.) plant architecture, because leaf angle strongly affects leaf direction and rice production, with more‐erect leaves being advantageous for high‐density plantings. The degree of leaf bending depends on the morphology of the lamina joint, which connects the leaf and the sheath. In this review, we discuss cell morphology in different lamina joint tissues and describe the underlying genetic network that governs this morphology and thus regulates leaf direction. Furthermore, we focus on the mechanism by how environmental factors influence rice leaf angle. Our review provides a theoretical framework for the future genetic improvement of rice leaf orientation and plant architecture.
In this review, we discuss cell morphology in different lamina joint tissues of rice and describe the underlying genetic network that governs this morphology and thus regulates leaf angle. Furthermore, we focus on the mechanism by how environmental factors influence rice lamina joint, then leaf direction and plant architecture.
The MADS box transcription factors are critical regulators of rice (Oryza sativa) reproductive development. Here, we here report the functional characterization of a rice MADS box family member, ...MADS29, which is preferentially expressed in the nucellus and the nucellar projection. Suppressed expression of MADS29 resulted in abnormal seed development; the seeds were shrunken, displayed a low grain-filling rate and suppressed starch biosynthesis, and contained abnormal starch granules. Detailed analysis indicated that the abnormal seed development is due to defective programmed cell death (PCD) of the nucellus and nucellar projection, which was confirmed by a TUNEL assay and transcriptome analysis. Further studies showed that expression of MADS29 is induced by auxin and MADS29 protein binds directly to the putative promoter regions of genes that encode a Cys protease and nucleotide binding site-Leu-rich repeat proteins, thereby stimulating the PCD. This study identifies MADS29 as a key regulator of early rice seed development by regulating the PCD of maternal tissues. It provides informative clues to elucidate the regulatory mechanism of maternal tissue degradation after fertilization and to facilitate the studies of endosperm development and seed filling.
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