TSPO-induced degradation of the ethylene receptor RhETR3 promotes salt tolerance in rose (Rosa hybrida).

The gaseous plant hormone ethylene regulates plant development, growth, and responses to stress. In particular, ethylene affects tolerance to salinity; however, the underlying mechanisms of ethylene signaling and salt tolerance are not fully understood. Here, we demonstrate that salt stress induces the degradation of the ethylene receptor ETHYLENE RESPONSE 3 (RhETR3) in rose (Rosa hybrid). Furthermore, the TspO/MBR (Tryptophan-rich sensory protein/mitochondrial benzodiazepine receptor) domain-containing membrane protein RhTSPO interacted with RhETR3 to promote its degradation in response to salt stress. Salt tolerance is enhanced in RhETR3-silenced rose plants but decreased in RhTSPO-silenced plants. The improved salt tolerance of RhETR3-silenced rose plants is partly due to the increased expression of ACC SYNTHASE1 (ACS1) and ACS2, which results in an increase in ethylene production, leading to the activation of ETHYLENE RESPONSE FACTOR98 (RhERF98) expression and, ultimately accelerating H2O2 scavenging under salinity conditions. Additionally, overexpression of RhETR3 increased the salt sensitivity of rose plants. Co-overexpression with RhTSPO alleviated this sensitivity. Together, our findings suggest that RhETR3 degradation is a key intersection hub for the ethylene signalling-mediated regulation of salt stress.

Transcriptomic profiling of rose flower under treatment of various phytohormones and plant growth regulators.

Rose is one of the most important ornamental plants, accounting for one-third of the world's fresh cut flower market. The vase life refers to the period of a cut flower retaining its appearance in a vase. During this period, the rose was subjected to a variety of abiotic and biotic stresses, resulting in a reduction in the life of cut flowers. Numerous studies have been carried out on cut rose, which proves the effects of various plant hormones on post-harvest dehydration, petal senescence and abscission, disease and vase life of cut rose flowers. In addition, the natural or synthetic hormones or its inhibitor have been successfully used in cut flower preservatives to extend the vase life of rose. However, there is still a lack of systematic and in-depth research on the expression of rose genes related to plant hormone response. Here we analyzed the gene expression changes of the rose flower under treatment of 11 different plant hormones or its inhibitors in order to provide reference for rose studies.

RhWRKY33 Positively Regulates Onset of Floral Senescence by Responding to Wounding- and Ethylene-Signaling in Rose Plants.

Rose plants are one of the most important horticultural crops, whose commercial value mainly depends on long-distance transportation, and wounding and ethylene are the main factors leading to their quality decline and accelerated senescence in the process. However, underlying molecular mechanisms of crosstalk between wounding and ethylene in the regulation of flower senescence remain poorly understood. In relation to this, transcriptome analysis was performed on rose flowers subjected to various treatments, including control, wounding, ethylene, and wounding- and ethylene- (EW) dual treatment. A large number of differentially expressed genes (DEGs) were identified, ranging from 2,442 between the ethylene- and control-treated groups to 4,055 between the EW- and control-treated groups. Using weighted gene co-expression network analysis (WGCNA), we identified a hub gene RhWRKY33 (rchiobhmchr5g0071811), accumulated in the nucleus, where it may function as a transcription factor. Moreover, quantitative reverse transcription PCR (RT-qPCR) results showed that the expression of RhWRKY33 was higher in the wounding-, ethylene, and EW-treated petals than in the control-treated petals. We also functionally characterized the RhWRKY33 gene through virus-induced gene silencing (VIGS). The silencing of RhWRKY33 significantly delayed the senescence process in the different treatments (control, wounding, ethylene, and EW). Meanwhile, we found that the effect of RhWRKY33-silenced petals under ethylene and EW dual-treatment were stronger than those under wounding treatment in delaying the petal senescence process, implying that RhWRKY33 is closely involved with ethylene and wounding mediated petal senescence. Overall, the results indicate that RhWRKY33 positively regulates the onset of floral senescence mediated by both ethylene and wounding signaling, but relies heavily on ethylene signaling.

Erratum: Author Correction: RhMYB108, an R2R3-MYB transcription factor, is involved in ethylene- and JA-induced petal senescence in rose plants.

[This corrects the article DOI: 10.1038/s41438-019-0221-8.].

RhMYB108, an R2R3-MYB transcription factor, is involved in ethylene- and JA-induced petal senescence in rose plants.

Rose (Rosa hybrida) plants are major ornamental species worldwide, and their commercial value greatly depends on their open flowers, as both the quality of fully open petals and long vase life are important. Petal senescence can be started and accelerated by various hormone signals, and ethylene is considered an accelerator of petal senescence in rose. To date, however, the underlying mechanism of signaling crosstalk between ethylene and other hormones such as JA in petal senescence remains largely unknown. Here, we isolated RhMYB108, an R2R3-MYB transcription factor, which is highly expressed in senescing petals as well as in petals treated with exogenous ethylene and JA. Applications of exogenous ethylene and JA markedly accelerated petal senescence, while the process was delayed in response to applications of 1-MCP, an ethylene action inhibitor. In addition, silencing of RhMYB108 alter the expression of SAGs such as RhNAC029, RhNAC053, RhNAC092, RhSAG12, and RhSAG113, and finally block ethylene- and JA-induced petal senescence. Furthermore, RhMYB108 was identified to target the promoters of RhNAC053, RhNAC092, and RhSAG113. Our results reveal a model in which RhMYB108 functions as a receptor of ethylene and JA signals to modulate the onset of petal senescence by targeting and enhancing senescence-associated gene expression.

The AP2/ERF transcription factor CmERF053 of chrysanthemum positively regulates shoot branching, lateral root, and drought tolerance.

KEY MESSAGE: We find that the DREB subfamily transcription factor, CmERF053, has a novel function to regulate the development of shoot branching and lateral root in addition to affecting abiotic stress. Dehydration-responsive element binding proteins (DREBs) are important plant transcription factors that regulate various abiotic stresses. Here, we isolated an APETALA2/ethylene-responsive factor (AP2/ERF) transcription factor from chrysanthemum (Chrysanthemum morifolium 'Jinba'), CmERF053, the expression of which was rapidly up-regulated by main stem decapitation. Phylogenetic analysis indicated that it belongs to the A-6 group of the DREB subfamily, and the subcellular localization assay confirmed that CmERF053 was a nuclear protein. Overexpression of CmERF053 in Arabidopsis exhibited positive effects of plant lateral organs, which had more shoot branching and lateral roots than did the wild type. We also found that the expression of CmERF053 in axillary buds was induced by exogenous cytokinins. These results suggested that CmERF053 may be involved in cytokinins-related shoot branching pathway. In this study, an altered auxin distribution was observed during root elongation in the seedlings of the overexpression plants. Furthermore, overexpress CmERF053 gene could enhance drought tolerance. Together, these findings indicated that CmERF053 plays crucial roles in regulating shoot branching, lateral root, and drought stress in plant. Moreover, our study provides potential application value for improving plant productivity, ornamental traits, and drought tolerance.

A Canonical DREB2-Type Transcription Factor in Lily Is Post-translationally Regulated and Mediates Heat Stress Response.

Based on studies of monocot crops and eudicot model plants, the DREB2 class of AP2-type transcription factor has been shown to play crucial roles in various abiotic stresses, especially in the upstream of the heat stress response; however, research on DREB2s has not been reported in non-gramineous monocot plants. Here, we identified a novel DREB2 (LlDREB2B) from lily (Lilium longiflorum), which was homologous to AtDREB2A of Arabidopsis, OsDREB2B of rice, and ZmDREB2A of maize. LlDREB2B was induced by heat, cold, salt, and mannitol stress, and its protein had transcriptional activity, was located in the nucleus, was able to bind to the dehydration-responsive element (DRE), and participated in the heat-responsive pathway of HsfA3. Overexpression of LlDREB2B in Arabidopsis activated expression of downstream genes and improved thermotolerance. LlDREB2B was not regulated by alternative splicing; functional transcripts accumulated under either normal or heat-stress conditions. A potential PEST sequence was predicted in LlDREB2B, but the stability of the LlDREB2B protein was not positively affected when the predicated PEST sequence was deleted. Further analysis revealed that the predicated PEST sequence lacked a SBC or SBC-like motif allowing interaction with BPMs and required for negative regulation. Nevertheless, LlDREB2B was still regulated at the post-translational level by interaction with AtDRIP1 and AtDRIP2 of Arabidopsis. In addition, LlDREB2B also interacted with AtRCD1 and LlRCD1 via a potential RIM motif located at amino acids 215-245. Taken together, our results show that LlDREB2B participated in the establishment of thermotolerance, and its regulation was different from that of the orthologs of gramineous and eudicot plants.

Thidiazuron Triggers Morphogenesis in Rosa canina L. Protocorm-Like Bodies by Changing Incipient Cell Fate.

Thidiazuron (N-phenyl-N'-1,2,3-thiadiazol-5-ylurea; TDZ) is an artificial plant growth regulator that is widely used in plant tissue culture. Protocorm-like bodies (PLBs) induced by TDZ serve as an efficient and rapid in vitro regeneration system in Rosa species. Despite this, the mechanism of PLB induction remains relatively unclear. TDZ, which can affect the level of endogenous auxins and cytokinins, converts the cell fate of rhizoid tips and triggers PLB formation and plantlet regeneration in Rosa canina L. In callus-rhizoids, which are rhizoids that co-develop from callus, auxin and a Z-type cytokinin accumulated after applying TDZ, and transcription of the auxin transporter gene RcPIN1 was repressed. The expression of RcARF4, RcRR1, RcCKX2, RcCKX3, and RcLOG1 increased in callus-rhizoids and rhizoid tips while the transcription of an auxin response factor (RcARF1) and auxin transport proteins (RcPIN2, RcPIN3) decreased in callus-rhizoids but increased in rhizoid tips. In situ hybridization of rhizoids showed that RcWUS and RcSERK1 were highly expressed in columella cells and root stem cells resulting in the conversion of cell fate into shoot apical meristems or embryogenic callus. In addition, transgenic XVE::RcWUS lines showed repressed RcWUS overexpression while RcWUS had no effect on PLB morphogenesis. Furthermore, higher expression of the root stem cell marker RcWOX5 and root stem cell maintenance regulator genes RcPLT1 and RcPLT2 indicated the presence of a dedifferentiation developmental pathway in the stem cell niche of rhizoids. Viewed together, our results indicate that different cells in rhizoid tips acquired regeneration competence after induction by TDZ. A novel developmental pathway containing different cell types during PLB formation was identified by analyzing the endogenous auxin and cytokinin content. This study also provides a deeper understanding of the mechanisms underlying in vitro regeneration in Rosa.

Physiological controls of chrysanthemum DgD27 gene expression in regulation of shoot branching.

KEY MESSAGE: DgD27 was cloned from D. grandiflorum for the first time and played an important role in shoot branching of chrysanthemum. Shoot branching plays an important role in determining plant architecture. D27 was previously proven to be involved in the strigolactone biosynthetic pathway in rice, Arabidopsis, and Medicago. To investigate the role of D27 in shoot branching of chrysanthemum, we isolated the D27 homolog DgD27. Functional analysis showed that DgD27 was a plastid-localized protein that restored the phenotype of Arabidopsis d27-1. Gene expression analysis revealed that DgD27 was expressed at the highest levels in stem, and was up-regulated by exogenous auxin. Decapitation could down-regulate DgD27 expression, but this effect could be restored by exogenous auxin. DgD27 expression was significantly down-regulated by dark treatment in axillary buds. In addition, DgD27 transcripts produced rapid responses in shoots and roots under conditions of phosphate absence, but only mild variation in responses in buds, stems, and roots with low nitrogen treatment. DgBRC1 transcripts also showed the same response in buds under low nitrogen conditions. Under phosphate deficiency, indole-3-acetic acid (IAA) levels increased, zeatin riboside levels decreased, and abscisic acid (ABA) levels increased in the shoot, while both IAA and ABA levels increased in the shoot under low nitrogen treatments. Gibberellin acid levels were unaffected by phosphate deficiency and low nitrogen treatments. Taken together, these results demonstrated the diverse roles of DgD27 in response to physiological controls in chrysanthemum shoot branching.