Phosphorylation of RAV1/2 by KIN10 is essential for transcriptional activation of CAT6/7, which underlies oxidative stress response in cassava

KIN10-mediated HB16 protein phosphorylation and self-association improve cassava disease resistance by transcriptional activation of lignin biosynthesis genes

Cassava bacterial blight significantly affects cassava yield worldwide, while major cassava cultivars are susceptible to this disease. Therefore, it is crucial to identify cassava disease resistance gene networks and defence molecules for the genetic improvement of cassava cultivars. In this study, we found that MeHB16 transcription factor as a differentially expressed gene in cassava cultivars with contrasting disease resistance, positively modulated disease resistance by modulating defence molecule lignin accumulation. Further investigation showed that MeHB16 physically interacted with itself via the leucine-Zippe domain (L-Zip), which was necessary for the transcriptional activation of downstream lignin biosynthesis genes. In addition, protein kinase MeKIN10 directly interacted with MeHB16 to promote its phosphorylation at Ser6, which in turn enhanced MeHB16 self-association and downstream lignin biosynthesis. In summary, this study revealed the molecular network of MeKIN10-mediated MeHB16 protein phosphorylation improved cassava bacterial blight resistance by fine-tuning lignin biosynthesis and provides candidate genes and the defence molecule for improving cassava disease resistance.

Coat protein of cassava common mosaic virus targets RAV1 and RAV2 transcription factors to subvert immunity in cassava

Cassava common mosaic virus (CsCMV, genus Potexvirus) is a prevalent virus associated with cassava mosaic disease, so it is essential to elucidate the underlying molecular mechanisms of the coevolutionary arms race between viral pathogenesis and the cassava (Manihot esculenta Crantz) defense response. However, the molecular mechanism underlying CsCMV infection is largely unclear. Here, we revealed that coat protein (CP) acts as a major pathogenicity determinant of CsCMV via a mutant infectious clone. Moreover, we identified the target proteins of CP-related to abscisic acid insensitive3 (ABI3)/viviparous1 (VP1) (MeRAV1) and MeRAV2 transcription factors, which positively regulated disease resistance against CsCMV via transcriptional activation of melatonin biosynthetic genes (tryptophan decarboxylase 2 (MeTDC2), tryptamine 5-hydroxylase (MeT5H), N-aceylserotonin O-methyltransferase 1 (MeASMT1)) and MeCatalase6 (MeCAT6) and MeCAT7. Notably, the interaction between CP, MeRAV1, and MeRAV2 interfered with the protein phosphorylation of MeRAV1 and MeRAV2 individually at Ser45 and Ser44 by the protein kinase, thereby weakening the transcriptional activation activity of MeRAV1 and MeRAV2 on melatonin biosynthetic genes, MeCAT6 and MeCAT7 dependent on the protein phosphorylation of MeRAV1 and MeRAV2. Taken together, the identification of the CP-MeRAV1 and CP-MeRAV2 interaction module not only illustrates a molecular mechanism by which CsCMV orchestrates the host defense system to benefit its infection and development but also provides a gene network with potential value for the genetic improvement of cassava disease resistance.

Molecular identification and functional characterization of a transcription factor GeRAV1 from Gelsemium elegans

BACKGROUND

Gelsemium elegans is a traditional Chinese medicinal plant and temperature is one of the key factors affecting its growth. RAV (related to ABI3/VP1) transcription factor plays multiple roles in higher plants, including the regulation of plant growth, development, and stress response. However, RAV transcription factor in G. elegans has not been reported.

RESULTS

In this study, three novel GeRAV genes (GeRAV1-GeRAV3) were identified from the transcriptome of G. elegans under low temperature stress. Phylogenetic analysis showed that GeRAV1-GeRAV3 proteins were clustered into groups II, IV, and V, respectively. RNA-sequencing (RNA-seq) and real-time quantitative PCR (qRT-PCR) analyses indicated that the expression of GeRAV1 and GeRAV2 was increased in response to cold stress. Furthermore, the GeRAV1 gene was successfully cloned from G. elegans leaf. It encoded a hydrophilic, unstable, and non-secretory protein that contained both AP2 and B3 domains. The amino acid sequence of GeRAV1 protein shared a high similarity of 81.97% with Camptotheca acuminata CaRAV. Subcellular localization and transcriptional self-activation experiments demonstrated that GeRAV1 was a nucleoprotein without self-activating activity. The GeRAV1 gene was constitutively expressed in the leaves, stems, and roots of the G. elegans, with the highest expression levels in roots. In addition, the expression of the GeRAV1 gene was rapidly up-regulated under abscisic acid (ABA), salicylic acid (SA), and methyl jasmonate (MeJA) stresses, suggesting that it may be involved in hormonal signaling pathways. Moreover, GeRAV1 conferred improved cold and sodium chloride tolerance in Escherichia coli Rosetta cells.

CONCLUSIONS

These findings provided a foundation for further understanding on the function and regulatory mechanism of the GeRAV1 gene in response to low-temperature stress in G. elegans.

The RAV transcription factor TEMPRANILLO1 involved in ethylene-mediated delay of chrysanthemum flowering

TEMPRANILLO1 (TEM1) is a transcription factor belonging to related to ABI3 and VP1 family, which is also known as ethylene response DNA-binding factor 1 and functions as a repressor of flowering in Arabidopsis. Here, a putative homolog of AtTEM1 was isolated and characterized from chrysanthemum, designated as CmTEM1. Exogenous application of ethephon leads to an upregulation in the expression of CmTEM1. Knockdown of CmTEM1 promotes floral initiation, while overexpression of CmTEM1 retards floral transition. Further phenotypic observations suggested that CmTEM1 involves in the ethylene-mediated inhibition of flowering. Transcriptomic analysis established that expression of the flowering integrator CmAFL1, a member of the APETALA1/FRUITFULL subfamily, was downregulated significantly in CmTEM1-overexpressing transgenic plants compared with wild-type plants but was verified to be upregulated in amiR-CmTEM1 lines by quantitative RT-PCR. In addition, CmTEM1 is capable of binding to the promoter of the CmAFL1 gene to inhibit its transcription. Moreover, the genetic evidence supported the notion that CmTEM1 partially inhibits floral transition by targeting CmAFL1. In conclusion, these findings demonstrate that CmTEM1 acts as a regulator of ethylene-mediated delayed flowering in chrysanthemum, partly through its interaction with CmAFL1.

Banana MKK1 modulates fruit ripening via the MKK1-MPK6-3/11-4-bZIP21 module

The mitogen-activated protein kinase (MAPK) cascade consisting of MKKK, MKK, and MPK plays an indispensable role in various plant physiological processes. Previously, we showed that phosphorylation of MabZIP21 by MaMPK6-3 is involved in banana fruit ripening, but the regulatory mechanism by which MKK controls banana fruit ripening remains unclear. Here, ripening-induced MaMKK1 from banana fruit is characterized, and transiently overexpressing and silencing of MaMKK1 in banana fruit accelerates and inhibits fruit ripening, respectively, possibly by influencing phosphorylation and activity of MPK. MaMKK1 interacts with and phosphorylates MaMPK6-3 and MaMPK11-4 mainly at the pTEpY residues, resulting in MPK activation. MaMPK11-4 phosphorylates MabZIP21 to elevate its transcriptional activation ability. Transgenic tomato fruit expressing MabZIP21 ripen quickly with a concomitant increase in MabZIP21 phosphorylation. Additionally, MabZIP21 activates MaMPK11-4 and MaMKK1 transcription to form a regulatory feedback loop. Collectively, here we report a regulatory pathway of the MaMPK6-3/11-4-MabZIP21 module in controlling banana fruit ripening.

Nicotiana benthamiana XYLEM CYSTEINE PROTEASE genes facilitate tracheary element formation in interfamily grafting

Grafting is a plant propagation technique widely used in agriculture. A recent discovery of the capability of interfamily grafting in Nicotiana has expanded the potential combinations of grafting. In this study, we showed that xylem connection is essential for the achievement of interfamily grafting and investigated the molecular basis of xylem formation at the graft junction. Transcriptome and gene network analyses revealed gene modules for tracheary element (TE) formation during grafting that include genes associated with xylem cell differentiation and immune response. The reliability of the drawn network was validated by examining the role of the Nicotiana benthamiana XYLEM CYSTEINE PROTEASE (NbXCP) genes in TE formation during interfamily grafting. Promoter activities of NbXCP1 and NbXCP2 genes were found in differentiating TE cells in the stem and callus tissues at the graft junction. Analysis of a Nbxcp1;Nbxcp2 loss-of-function mutant indicated that NbXCPs control the timing of de novo TE formation at the graft junction. Moreover, grafts of the NbXCP1 overexpressor increased the scion growth rate as well as the fruit size. Thus, we identified gene modules for TE formation at the graft boundary and demonstrated potential ways to enhance Nicotiana interfamily grafting.

Deciphering peroxisomal reactive species interactome and redox signalling networks

Plant peroxisomes are highly dynamic organelles with regard to metabolic pathways, number and morphology and participate in different metabolic processes and cell responses to their environment. Peroxisomes from animal and plant cells house a complex system of reactive oxygen species (ROS) production associated to different metabolic pathways which are under control of an important set of enzymatic and non enzymatic antioxidative defenses. Nitric oxide (NO) and its derivate reactive nitrogen species (RNS) are also produced in these organelles. Peroxisomes can regulate ROS and NO/RNS levels to allow their role as signalling molecules. The metabolism of other reactive species such as carbonyl reactive species (CRS) and sulfur reactive species (SRS) in peroxisomes and their relationship with ROS and NO have not been explored in depth. In this review, we define a peroxisomal reactive species interactome (PRSI), including all reactive species ROS, RNS, CRS and SRS, their interaction and effect on target molecules contributing to the dynamic redox/ROS homeostasis and plasticity of peroxisomes, enabling fine-tuned regulation of signalling networks associated with peroxisome-dependent H₂O₂. Particular attention will be paid to update the information available on H₂O₂-dependent peroxisomal retrograde signalling and to discuss a specific peroxisomal footprint.

Fast Identification of In Vivo Protein Phosphorylation Events Using Transient Expression in Leaf Mesophyll Protoplasts and Phos-tagTM SDS-PAGE

Phosphorylation/dephosphorylation is a key posttranslational mechanism for signal transduction and amplification. Several techniques exist for assessing protein phosphorylation status, but each has its own drawbacks. The fast, straightforward, and low-tech approach described here uses transient overexpression of peptide-tagged proteins in Arabidopsis leaf mesophyll protoplasts and immunoblotting with Phos-tag™ SDS-PAGE and commercial anti-tag antibodies. We illustrate this with two relevant examples related to the SnRK1 protein kinase, which mediates metabolic stress signaling: Arabidopsis thaliana SnRK1 activation by T-loop (auto-)phosphorylation and SnRK1 phosphorylation of the Arabidopsis RAV1 transcription factor, which is involved in seed germination and early seedling development.

Genome-Wide Analysis of the RAV Gene Family in Wheat and Functional Identification of TaRAV1 in Salt Stress

RAV transcription factors (TFs) are unique to higher plants and contain both B3 and APETALA2 (AP2) DNA binding domains. Although sets of RAV genes have been identified from several species, little is known about this family in wheat. In this study, 26 RAV genes were identified in the wheat genome. These wheat RAV TFs were phylogenetically clustered into three classes based on their amino acid sequences. A TaRAV gene located on chromosome 1D was cloned and named TaRAV1. TaRAV1 was expressed in roots, stems, leaves, and inflorescences, and its expression was up-regulated by heat while down-regulated by salt, ABA, and GA. Subcellular localization analysis revealed that the TaRAV1 protein was localized in the nucleus. The TaRAV1 protein showed DNA binding activity in the EMSA assay and transcriptional activation activity in yeast cells. Overexpressing TaRAV1 enhanced the salt tolerance of Arabidopsis and upregulated the expression of SOS genes and other stress response genes. Collectively, our data suggest that TaRAV1 functions as a transcription factor and is involved in the salt stress response by regulating gene expression in the SOS pathway.