Functional analysis of the seven in absentia ubiquitin ligase family in tomato

A review on ubiquitin ligases: Orchestrators of plant resilience in adversity

Ubiquitin- proteasome system (UPS) is universally present in plants and animals, mediating many cellular processes needed for growth and development. Plants constantly defend themselves against endogenous and exogenous stimuli such as hormonal signaling, biotic stresses such as viruses, fungi, nematodes, and abiotic stresses like drought, heat, and salinity by developing complex regulatory mechanisms. Ubiquitination is a regulatory mechanism involving selective elimination and stabilization of regulatory proteins through the UPS system where E3 ligases play a central role; they can bind to the targets in a substrate-specific manner, followed by poly-ubiquitylation, and subsequent protein degradation by 26 S proteasome. Increasing evidence suggests different types of E3 ligases play important roles in plant development and stress adaptation. Herein, we summarize recent advances in understanding the regulatory roles of different E3 ligases and primarily focus on protein ubiquitination in plant-environment interactions. It also highlights the diversity and complexity of these metabolic pathways that enable plant to survive under challenging conditions. This reader-friendly review provides a comprehensive overview of E3 ligases and their substrates associated with abiotic and biotic stresses that could be utilized for future crop improvement.

The SINA1-BSD1 Module Regulates Vegetative Growth Involving Gibberellin Biosynthesis in Tomato

In plants, vegetative growth is controlled by synergistic and/or antagonistic effects of many regulatory factors. Here, the authors demonstrate that the ubiquitin ligase seven in absentia1 (SINA1) mammalian BTF2-like transcription factors, Drosophila synapse-associated proteins, and yeast DOS2-like proteins (BSD1) function as a regulatory module to control vegetative growth in tomato via regulation of the production of plant growth hormone gibberellin (GA). SINA1 negatively regulates the protein level of BSD1 through ubiquitin-proteasome-mediated degradation, and the transgenic tomato over-expressing SINA1 (SINA1-OX) resembles the dwarfism phenotype of the BSD1-knockout (BSD1-KO) tomato plant. BSD1 directly activates expression of the BSD1-regulated gene 1 (BRG1) via binding to a novel core BBS (standing for BSD1 binding site) binding motif in the BRG1 promoter. Knockout of BRG1 (BRG1-KO) in tomato also results in a dwarfism phenotype, suggesting BRG1 plays a positive role in vegetative growth as BSD1 does. Significantly, GA contents are attenuated in transgenic SINA1-OX, BSD1-KO, and BRG1-KO plants exhibiting dwarfism phenotype and exogenous application of bioactive GA3 restores their vegetative growth. Moreover, BRG1 is required for the expression of multiple GA biosynthesis genes and BSD1 activates three GA biosynthesis genes promoting GA production. Thus, this study suggests that the SINA1-BSD1 module controls vegetative growth via direct and indirect regulation of GA biosynthesis in tomato.

MdSINA2-MdNAC104 Module Regulates Apple Alkaline Resistance by Affecting γ-Aminobutyric Acid Synthesis and Transport

Soil alkalization is an adverse factor limiting plant growth and yield. As a signaling molecule and secondary metabolite, γ-aminobutyric acid (GABA) responds rapidly to alkaline stress and enhances the alkaline resistance of plants. However, the molecular mechanisms by which the GABA pathway adapts to alkaline stress remain unclear. In this study, a transcription factor, MdNAC104 is identified, from the transcriptome of the alkaline-stressed roots of apple, which effectively reduces GABA levels and negatively regulates alkaline resistance. Nevertheless, applying exogenous GABA compensates the negative regulatory mechanism of overexpressed MdNAC104 on alkaline resistance. Further research confirms that MdNAC104 repressed the GABA biosynthetic gene MdGAD1/3 and the GABA transporter gene MdALMT13 by binding to their promoters. Here, MdGAD1/3 actively regulates alkaline resistance by increasing GABA synthesis, while MdALMT13 promotes GABA accumulation and efflux in roots, resulting in an improved resistance to alkaline stress. This subsequent assays reveal that MdSINA2 interacts with MdNAC104 and positively regulates root GABA content and alkaline resistance by ubiquitinating and degrading MdNAC104 via the 26S proteasome pathway. Thus, the study reveals the regulation of alkaline resistance and GABA homeostasis via the MdSINA2-MdNAC104-MdGAD1/3/MdALMT13 module in apple. These findings provide novel insight into the molecular mechanisms of alkaline resistance in plants.

Genome-Wide Identification of Seven in Absentia E3 Ubiquitin Ligase Gene Family and Expression Profiles in Response to Different Hormones in Uncaria rhynchophylla

SINA (Seven in absentia) E3 ubiquitin ligases are a family of RING (really interesting new gene) E3 ubiquitin ligases, and they play a crucial role in regulating plant growth and development, hormone response, and abiotic and biotic stress. However, there is little research on the SINA gene family in U. rhynchophylla. In this study, a total of 10 UrSINA genes were identified from the U. rhynchophylla genome. The results of multiple sequence alignments and chromosomal locations show that 10 UrSINA genes were unevenly located on 22 chromosomes, and each UrSINA protein contained a SINA domain at the N-terminal and RING domains at the C-terminal. Synteny analysis showed that there are no tandem duplication gene pairs and there are four segmental gene pairs in U. rhynchophylla, contributing to the expansion of the gene family. Furthermore, almost all UrSINA genes contained the same gene structure, with three exons and two introns, and there were many cis-acting elements relating to plant hormones, light responses, and biotic and abiotic stress. The results of qRT-PCR show that most UrSINA genes were expressed in stems, with the least expression in roots; meanwhile, most UrSINA genes and key enzyme genes were responsive to ABA and MeJA hormones with overlapping but different expression patterns. Co-expression analysis showed that UrSINA1 might participate in the TIA pathway under ABA treatment, and UrSINA5 and UrSINA6 might participate in the TIA pathway under MeJA treatment. The mining of UrSINA genes in the U. rhynchophylla provided novel information for understanding the SINA gene and its function in plant secondary metabolites, growth, and development.

Genomic-wide analysis reveals seven in absentia genes regulating grain development in wheat (Triticum aestivum L.)

Seven in absentia proteins, which contain a conserved SINA domain, are involved in regulating various aspects of wheat (Triticum aestivum L.) growth and development, especially in response to environmental stresses. However, it is unclear whether TaSINA family members are involved in regulating grain development until now. In this study, the expression pattern, genomic polymorphism, and relationship with grain-related traits were analyzed for all TaSINA members. Most of the TaSINA genes identified showed higher expression levels in young wheat spikes or grains than other organs. The genomic polymorphism analysis revealed that at least 62 TaSINA genes had different haplotypes, where the haplotypes of five genes were significantly correlated with grain-related traits. Kompetitive allele-specific PCR markers were developed to confirm the single nucleotide polymorphisms in TaSINA101 and TaSINA109 among the five selected genes in a set of 292 wheat accessions. The TaSINA101-Hap II and TaSINA109-Hap II haplotypes had higher grain weight and width compared to TaSINA101-Hap I and TaSINA109-Hap I in at least three environments, respectively. The qRT-PCR assays revealed that TaSINA101 was highly expressed in the palea shell, seed coat, and embryo in young wheat grains. The TaSINA101 protein was unevenly distributed in the nucleus when transiently expressed in the protoplast of wheat. Three homozygous TaSINA101 transgenic lines in rice (Oryza sativa L.) showed higher grain weight and size compared to the wild type. These findings provide valuable insight into the biological function and elite haplotype of TaSINA family genes in wheat grain development at a genomic-wide level.

Genetic variation in ZmKW1 contributes to kernel weight and size in dent corn and popcorn

Kernel weight is a critical factor that essentially affects maize (Zea mays) yield. In natural inbred lines, popcorn kernels exhibit overtly smaller sizes compared to dent corn kernels, and kernel weight, which is controlled by multiple genetic loci, varies widely. Here, we characterized a major quantitative trait locus on chromosome 1, responsible for controlling kernel weight (qKW1) and size. The qKW1 locus encodes a protein containing a seven in absentia domain with E3 ubiquitin ligase activity, expressed prominently from the top to the middle region of the endosperm. The presence and function of qKW1 were confirmed through ZmKW1 gene editing, where the mutations in ZmKW1 within dent corn significantly increased kernel weight, consistent with alterations in kernel size, while overexpression of ZmKW1 had the opposite effect. ZmKW1 acts as a negative regulator of kernel weight and size by reducing both the number and size of the endosperm cells and impacting endosperm filling. Notably, the popcorn allele qKW1N and the dent corn allele qKW1D encode identical proteins; however, the differences in promoter activity arise due to the insertion of an Indel-1346 sequence in the qKW1N promoter, resulting in higher expression levels compared to qKW1D, thus contributing to the variation in kernel weight and size between popcorn and dent corn kernels. Linkage disequilibrium analysis of the 2.8 kb promoter region of ZmKW1 in a dataset comprising 111 maize association panels identified two distinct haplotypes. Our results provide insight into the mechanisms underlying kernel development and yield regulation in dent corn and popcorn, with a specific focus on the role of the ubiquitination system.

New Advances in the Study of Regulation of Tomato Flowering-Related Genes Using Biotechnological Approaches

The tomato is a convenient object for studying reproductive processes, which has become a classic. Such complex processes as flowering and fruit setting require an understanding of the fundamental principles of molecular interaction, the structures of genes and proteins, the construction of signaling pathways for transcription regulation, including the synchronous actions of cis-regulatory elements (promoter and enhancer), trans-regulatory elements (transcription factors and regulatory RNAs), and transposable elements and epigenetic regulators (DNA methylation and acetylation, chromatin structure). Here, we discuss the current state of research on tomatoes (2017-2023) devoted to studying the function of genes that regulate flowering and signal regulation systems using genome-editing technologies, RNA interference gene silencing, and gene overexpression, including heterologous expression. Although the central candidate genes for these regulatory components have been identified, a complete picture of their relationship has yet to be formed. Therefore, this review summarizes the latest achievements related to studying the processes of flowering and fruit set. This work attempts to display the gene interaction scheme to better understand the events under consideration.

In silico analysis of the Seven IN Absentia (SINA) genes in bread wheat sheds light on their structure in plants

Seven IN Absentia (SINA) is a small family of genes coding for ubiquitin-ligases that play major roles in regulating various plant growth and developmental processes, as well as in plant response to diverse biotic and abiotic stresses. Here, we studied the SINA genes family in bread wheat Triticum aestivum which is a culture of major importance for food security worldwide. One hundred and forty-one SINA family genes have been identified in bread wheat and showed that their number is very high compared to other plant species such as A. thaliana or rice. The expansion of this family seems to have been more important in monocots than in eudicots. In bread wheat, the chromosome 3 distal region is the site of a massive amplification of the SINA family, since we found that 83 of the 141 SINA genes are located on this chromosome in the Chinese Spring variety. This amplification probably occurred as a result of local duplications, followed by sequences divergence. The study was then extended to 4856 SINA proteins from 97 plant species. Phylogenetic and structural analyses identified a group of putative ancestral SINA proteins in plants containing a 58 aminoacid specific signature. Based on sequence homology and the research of that "Ancestral SINA motif" of 58 amino acids, a methodological process has been proposed and lead to the identification of functional SINA genes in a large family such as the Triticae that might be used for other species. Finally, tis paper gives a comprehensive overview of wheat gene family organization and functionalization taken the SINA genes as an example.

TaSINA2B, interacting with TaSINA1D, positively regulates drought tolerance and root growth in wheat (Triticum aestivum L.)

Wheat (Triticum aestivum L.) is an important food crop mainly grown in arid and semiarid regions worldwide, whose productivity is severely limited by drought stress. Although various E3 ubiquitin (Ub) ligases regulate drought stress, only a few SINA-type E3 Ub ligases are known to participate in such responses. Herein, we identified and cloned 15 TaSINAs from wheat. The transcription level of TaSINA2B was highly induced by drought, osmotic and abscisic acid treatments. Two-type promoters of TaSINA2B were found in 192 wheat accessions; furthermore wheat accessions with promoter TaSINA2BII showed a considerably higher level of drought tolerance and gene expression levels than those characterizing accessions with promoter TaSINA2BI that was mainly caused by a 64 bp insertion in its promoter. Enhanced drought tolerance of TaSINA2B-overexpressing (OE) transgenic wheat lines was found to be associated with root growth promotion. Further, an interaction between TaSINA2B and TaSINA1D was detected through yeast two-hybrid and bimolecular fluorescence complementation assays. And TaSINA1D-OE transgenic wheat lines showed similar drought tolerance and root growth phenotype to those observed when TaSINA2B was overexpressed. Therefore, the variation of TaSINA2B promoter contributed to the drought stress regulation, while TaSINA2B, interacting with TaSINA1D, positively regulated drought tolerance by promoting root growth.

The extensin protein SAE1 plays a role in leaf senescence and is targeted by the ubiquitin ligase SINA4 in tomato

Extensins are hydroxyproline-rich glycoproteins and generally play a structural role in cell wall integrity. In this study, we determined a novel role of tomato (Solanum lycopersicum) SENESCENCE-ASSOCIATED EXTENSIN1 (SAE1) in leaf senescence. Both gain- and loss-of-function analyses suggest that SAE1 plays a positive role in leaf senescence in tomato. Transgenic plants overexpressing SAE1 (SAE1-OX) exhibited premature leaf senescence and enhanced dark-induced senescence, whereas SAE1 knockout (SAE1-KO) plants displayed delayed development-dependent and dark-induced leaf senescence. Heterologous overexpression of SlSAE1 in Arabidopsis also led to premature leaf senescence and enhanced dark-induced senescence. In addition, the SAE1 protein was found to interact with the tomato ubiquitin ligase SlSINA4, and SlSINA4 promoted SAE1 degradation in a ligase-dependent manner when co-expressed in Nicotiana benthamiana leaves, suggesting that SlSINA4 controls SAE1 protein levels via the ubiquitin-proteasome pathway. Introduction of an SlSINA4-overexpression construct into the SAE1-OX tomato plants consistently completely eliminated accumulation of the SAE1 protein and suppressed the phenotypes conferred by overexpression of SAE1. Taken together, our results suggest that the tomato extensin SAE1 plays a positive role in leaf senescence and is regulated by the ubiquitin ligase SINA4.

Extensin and senescence: a cell wall connection

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Lu H, Niu X, Fan Y, Yuan Y, Huang L, Zhao B, Liu Y, Xiao F. 2023. The extensin protein SAE1 plays a role in leaf senescence and is targeted by the ubiquitin ligase SINA4 in tomato. Journal of Experimental Botany 74, 5635–5652.

Genome-wide characterization of SINA E3 ubiquitin ligase family members and their expression profiles in response to various abiotic stresses and hormones in kiwifruit

SINA (Seven in absentia) proteins in the subtype of E3 ubiquitin ligase family have important functions in regulating the growth and development as well as in response to abiotic and biotic stresses in plants. However, the characteristics and possible functions of SINA family proteins in kiwifruit are not studied. In this research, a total number of 11 AcSINA genes in the kiwifruit genome were identified. Chromosome location and multiple sequence alignment analyses indicated that they were unevenly distributed on 10 chromosomes and all contained the typical N-terminal RING domain and C-terminal SINA domain. Phylogenetic, gene structure and collinear relationship analyses revealed that they were highly conserved with the same gene structure, and have gone through segmental duplication events. Expression pattern analyses demonstrated that all AcSINAs were ubiquitously expressed in roots, stems and leaves, and were responsive to different abiotic and plant hormone treatments with overlapped but distinct expression patterns. Further yeast two-hybrid and Arabidopsis transformation analyses demonstrated most AcSINAs interacted with itself or other AcSINA members to form homo- or heterodimers, and ectopic expression of AcSINA2 in Arabidopsis led to hypersensitive growth phenotype of transgenic seedlings to ABA treatment. Our results reveal that AcSINAs take part in the response to various abiotic stresses and hormones, and provide important information for the functional elucidation of AcSINAs in vine fruit plants.

GhSINA1, a SEVEN in ABSENTIA ubiquitin ligase, negatively regulates fiber development in Upland cotton

Protein ubiquitination is essential for plant growth and responses to the environment. The SEVEN IN ABSENTIA (SINA) ubiquitin ligases have been extensively studied in plants, but information on their roles in fiber development is limited. Here, we identified GhSINA1 in Upland cotton (Gossypium hirsutum), which has a conserved RING finger domain and SINA domain. Quantitative real-time PCR (qRT-PCR) analysis showed that GhSINA1 was preferentially expressed during fiber initiation and elongation, especially during initiation in the fuzzless-lintless cotton mutant. Subcellular localization experiments indicated that GhSINA1 localized to the nucleus. In vitro ubiquitination analysis revealed that GhSINA1 has E3 ubiquitin ligase activity. Ectopic overexpression of GhSINA1 in Arabidopsis thaliana reduced the number and length of root hairs and trichomes. Yeast two-hybrid (Y2H), firefly luciferase complementation imaging (LCI), and bimolecular fluorescence complementation (BiFC) assays demonstrated that the GhSINA1 proteins could interact with each other to form homodimers and heterodimers. Overall, these results suggest that GhSINA1 may act as a negative regulator in cotton fiber development through homodimerization and heterodimerization.

Tomato SlSTK is involved in glucose response and regulated by the ubiquitin ligase SlSINA4

Glucose signaling plays an essential role in plant growth, development and stress response. Previous studies have shown that STOREKEEPER (STK) is a new class of DNA binding protein that regulates patatin expression in potato tubers and confers elevated sensitivity to glucose response in Arabidopsis thaliana. However, the biological functions of STK gene in tomato (Solanum lycopersicum) have not been studied. Here, we characterized the tomato SlSTK and determined its role in glucose signaling. The SlSTK protein was localized in the nucleus and the expression of the SlSTK gene was induced by the glucose treatment. Overexpression of SlSTK in tomato enhanced glucose sensitivity, as manifested by reduced seed germination rate and arrested growth at the early seedling stage. In contrast, the SlSTK-knockout plants generated via the clustered regularly interspaced short palindromic repeats (CRISPR) - CRISPR-associated protein 9 (CRISPR-Cas9) technique attenuated the sensitivity to glucose. In addition, SlSTK was ubiquitinated in plant cells and interacted with the tomato ubiquitin ligase SEVEN IN ABSENTIA4 (SlSINA4) that degrades SlSTK in a ligase-dependent manner. Taken together, these results suggest that SlSTK is involved in glucose signaling and its stability is regulated by the ubiquitin ligase SlSINA4.

Characterization of RING-type ubiquitin SINA E3 ligases and their responsive expression to salt and osmotic stresses in Brassica napus

SINA (Seven in absentia) proteins in the subtype of E3 ubiquitin ligase family play a crucial role in plant growth and development. However, their functions in response to salt and osmotic stresses in oil crops are still largely unknown. In this study, a total number of 23 BnaSINAs were identified in the rapeseed genome. Chromosome location and collinear relationship analyses revealed that they were unevenly distributed on 13 chromosomes, and have gone through 22 segmental duplication events under purifying selection. Phylogenetic and gene structural analyses indicated that they belonged to five main groups, and those in the same subgroup showed similar gene structure. All BnaSINAs were predicted to form homo- or heterodimers. Except BnaSINA7, BnaSINA11, BnaSINA17 and BnaSINA18, which lacked the N-terminal RING finger, all BnaSINAs contained a conserved C-terminal SINA domain, a typical structural feature of the RING-type E3 ligase family. Transcriptional expression analyses demonstrated that most BnaSINAs were ubiquitously expressed in roots, stems, leaves, flowers, pods and seeds, and all were responsive to salt and osmotic stresses. Further, yeast two-hybrid and Arabidopsis mutant complementation analyses demonstrated that BnaSINA4 interacted with BnaSINA17 to form heterodimer, and expression of BnaSINA17 in the Arabidopsis sina2 mutant restored its growth resistance to salt and osmotic stresses. Our findings provide an important genetic foundation for the functional elucidation of BnaSINAs and a novel gene resource for the breeding of new oil crop cultivars with improved abiotic stress resistance.

Puncta-localized TRAF domain protein TC1b contributes to the autoimmunity of snc1

Immune receptors play important roles in the perception of pathogens and initiation of immune responses in both plants and animals. Intracellular nucleotide-binding domain leucine-rich repeat (NLR)-type receptors constitute a major class of receptors in vascular plants. In the Arabidopsis thaliana mutant suppressor of npr1-1, constitutive 1 (snc1), a gain-of-function mutation in the NLR gene SNC1 leads to SNC1 overaccumulation and constitutive activation of defense responses. From a CRISPR/Cas9-based reverse genetics screen in the snc1 autoimmune background, we identified that mutations in TRAF CANDIDATE 1b (TC1b), a gene encoding a protein with four tumor necrosis factor receptor-associated factor (TRAF) domains, can suppress snc1 phenotypes. TC1b does not appear to be a general immune regulator as it is not required for defense mediated by other tested immune receptors. TC1b also does not physically associate with SNC1, affect SNC1 accumulation, or affect signaling of the downstream helper NLRs represented by ACTIVATED DISEASE RESISTANCE PROTEIN 1-L2 (ADR1-L2), suggesting that TC1b impacts snc1 autoimmunity in a unique way. TC1b can form oligomers and localizes to punctate structures of unknown function. The puncta localization of TC1b strictly requires its coiled-coil (CC) domain, whereas the functionality of TC1b requires the four TRAF domains in addition to the CC. Overall, we uncovered the TRAF domain protein TC1b as a novel positive contributor to plant immunity.

Apple SINA E3 ligase MdSINA3 negatively mediates JA-triggered leaf senescence by ubiquitinating and degrading the MdBBX37 protein

Jasmonic acid (JA) induces chlorophyll degradation and leaf senescence. B-box (BBX) proteins play important roles in the modulation of leaf senescence, but the molecular mechanism of BBX protein-mediated leaf senescence remains to be further studied. Here, we identified the BBX protein MdBBX37 as a positive regulator of JA-induced leaf senescence in Malus domestica (apple). Further studies showed that MdBBX37 interacted with the senescence regulatory protein MdbHLH93 to enhance its transcriptional activation on the senescence-associated gene MdSAG18, thereby promoting leaf senescence. Moreover, the JA signaling repressor MdJAZ2 interacted with MdBBX37 and interfered with the interaction between MdBBX37 and MdbHLH93, thereby negatively mediating MdBBX37-promoted leaf senescence. In addition, the E3 ubiquitin ligase MdSINA3 delayed MdBBX37-promoted leaf senescence through targeting MdBBX37 for degradation. The MdJAZ2-MdBBX37-MdbHLH93-MdSAG18 and MdSINA3-MdBBX37 modules realized the precise modulation of JA on leaf senescence. In parallel, our data demonstrate that MdBBX37 was involved in abscisic acid (ABA)- and ethylene-mediated leaf senescence through interacting with the ABA signaling regulatory protein MdABI5 and ethylene signaling regulatory protein MdEIL1, respectively. Taken together, our results not only reveal the role of MdBBX37 as an integration node in JA-, ABA- and ethylene-mediated leaf senescence, but also provide new insights into the post-translational modification of BBX proteins.

TRAF proteins as key regulators of plant development and stress responses

Tumor necrosis factor receptor-associated factor (TRAF) proteins are conserved in higher eukaryotes and play key roles in transducing cellular signals across different organelles. They are characterized by their C-terminal region (TRAF-C domain) containing seven to eight anti-parallel β-sheets, also known as the meprin and TRAF-C homology (MATH) domain. Over the past few decades, significant progress has been made toward understanding the diverse roles of TRAF proteins in mammals and plants. Compared to other eukaryotic species, the Arabidopsis thaliana and rice (Oryza sativa) genomes encode many more TRAF/MATH domain-containing proteins; these plant proteins cluster into five classes: TRAF/MATH-only, MATH-BPM, MATH-UBP (ubiquitin protease), Seven in absentia (SINA), and MATH-Filament and MATH-PEARLI-4 proteins, suggesting parallel evolution of TRAF proteins in plants. Increasing evidence now indicates that plant TRAF proteins form central signaling networks essential for multiple biological processes, such as vegetative and reproductive development, autophagosome formation, plant immunity, symbiosis, phytohormone signaling, and abiotic stress responses. Here, we summarize recent advances and highlight future prospects for understanding on the molecular mechanisms by which TRAF proteins act in plant development and stress responses.

Rice SIAH E3 Ligases Interact with RMD Formin and Affect Plant Morphology

Formins are actin-binding proteins that are key to maintaining the actin cytoskeleton in cells. However, molecular mechanisms controlling the stability of formin proteins in plants remain unknown. Here, we have identified six rice SIAH-type E3 ligases, named RIP1-6 (RMD Interacting Protein 1-6) respectively, with ubiquitination enzyme activity in vitro. All six proteins can form homo- and hetero-dimers with themselves, and hetero-dimers with type II formin RMD/OsFH5. In vivo assays showed that RIP1-6 proteins localize in the cytoplasm with a punctate distribution, and all of them interact with RMD to change its native diffuse cytoplasmic localization to match that of RIP1-6. To our surprise, degradation experiments revealed that RIP1, RIP5, and RIP6 decrease rather than increase the degradation rate of RMD. Genetic analyses revealed redundancy between these six genes; either single or double mutants did not show any obvious phenotypes. However, the sextuple rip1-6 mutant displayed dwarf height, wrinkled seeds and wider leaves that were similar to the previously reported rmd mutant, and defective microfilaments and increased flag leaf angles that were not reported in rmd mutant. Collectively, our study provides insights into the mechanisms determining formin protein stability in plants.

The wheat Seven in absentia gene is associated with increases in biomass and yield in hot climates

Wheat (Triticum aestivum L.) productivity is severely reduced by high temperatures. Breeding of heat-tolerant cultivars can be achieved by identifying genes controlling physiological and agronomical traits when high temperatures occur and using these to select superior genotypes, but no gene underlying genetic variation for heat tolerance has previously been described. We advanced the positional cloning of qYDH.3BL, a quantitative trait locus (QTL) on bread wheat chromosome 3B associated with increased yield in hot and dry climates. The delimited genomic region contained 12 putative genes and a sequence variant in the promoter region of one gene, Seven in absentia, TaSINA. This was associated with the QTL's effects on early vigour, root growth, plant biomass, and yield components in two distinct wheat populations grown under various growth conditions. Near isogenic lines carrying the positive allele at qYDH.3BL underexpressed TaSINA and had increased vigour and water use efficiency early in development, as well as increased biomass, grain number, and grain weight following heat stress. A survey of worldwide distribution indicated that the positive allele became widespread from the 1950s through the CIMMYT wheat breeding programme but, to date, has been selected only in breeding programmes in Mexico and Australia.

SEVEN IN ABSENTIA Ubiquitin Ligases Positively Regulate Defense Against Verticillium dahliae in Gossypium hirsutum

Ubiquitination is a post-translational regulatory mechanism that controls a variety of biological processes in plants. The E3 ligases confer specificity by recognizing target proteins for ubiquitination. Here, we identified SEVEN IN ABSENTIA (SINA) ubiquitin ligases, which belong to the RING-type E3 ligase family, in upland cotton (Gossypium hirsutum). Twenty-four GhSINAs were characterized, and the expression levels of GhSINA7, GhSINA8, and GhSINA9 were upregulated at 24 h after inoculation with Verticillium dahliae. In vitro ubiquitination assays indicated that the three GhSINAs possessed E3 ubiquitin ligase activities. Transient expression in Nicotiana benthamiana leaves showed that they localized to the nucleus. And yeast two-hybrid (Y2H) screening revealed that they could interact with each other. The ectopic overexpression of GhSINA7, GhSINA8, and GhSINA9 independently in Arabidopsis thaliana resulted in increased tolerance to V. dahliae, while individual knockdowns of GhSINA7, GhSINA8, and GhSINA9 compromised cotton resistance to the pathogen. Thus, GhSINA7, GhSINA8, and GhSINA9 act as positive regulators of defense responses against V. dahliae in cotton plants.

Genome-Wide Identification of Apple Ubiquitin SINA E3 Ligase and Functional Characterization of MdSINA2

SINA (Seven in absentia) proteins are a small family of ubiquitin ligases that play important roles in regulating plant growth and developmental processes as well as in responses to diverse types of biotic and abiotic stress. However, the characteristics of the apple SINA family have not been previously studied. Here, we identified 11 MdSINAs members in the apple genome based on their conserved, N-terminal RING and C-terminal SINA domains. We also reconstructed a phylogeny of these genes; characterized their chromosomal location, structure, and motifs; and identified two major groups of MdSINA genes. Subsequent qRT-PCR analyses were used to characterize the expression of MdSINA genes in various tissues and organs, and levels of expression were highest in leaves. MdSINAs were significantly induced under ABA and carbon- and nitrate-starvation treatment. Except for MdSINA1 and MdSINA7, the other MdSINA proteins could interact with each other. Moreover, MdSINA2 was found to be localized in the nucleus using Agrobacterium-mediated transient expression. Western-blot analysis showed that MdSINA2 accumulated extensively under light, decreased under darkness, and became insensitive to light when the RING domain was disrupted. Finally, ABA-hypersensitive phenotypes were confirmed by transgenic calli and the ectopic expression of MdSINA2 in Arabidopsis. In conclusion, our results suggest that MdSINA genes participate in the responses to different types of stress, and that MdSINA2 might act as a negative regulator in the ABA stress response.