SUMMARY
Jasmonate (JA) induces the biosynthesis of anthocyanin and proanthocyanidin. MdMYB9 is essential for modulating the accumulation of both anthocyanin and proanthocyanidin in apple, but the ...molecular mechanism for induction of anthocyanin and proanthocyanidin biosynthesis by JA is unclear. In this study, we discovered an apple telomere‐binding protein (MdTRB1) to be the interacting protein of MdMYB9. A series of biological assays showed that MdTRB1 acted as a positive modulator of anthocyanin and proanthocyanidin accumulation, and is dependent on MdMYB9. MdTRB1 interacted with MdMYB9 and enhanced the activation activity of MdMYB9 to its downstream genes. In addition, we found that the JA signaling repressor MdJAZ1 interacted with MdTRB1 and interfered with the interaction between MdTRB1 and MdMYB9, therefore negatively modulating MdTRB1‐promoted biosynthesis of anthocyanin and proanthocyanidin. These results show that the JAZ1–TRB1–MYB9 module dynamically modulates JA‐mediated accumulation of anthocyanin and proanthocyanidin. Taken together, our data further expand the functional study of TRB1 and provide insights for further studies of the modulation of anthocyanin and proanthocyanidin biosynthesis by JA.
Significance Statement
The apple telomere‐binding protein MdTRB1 positively modulates JA‐mediated accumulation of anthocyanin and proanthocyanidin by interacting with MdMYB9 and enhancing the activation activity of MdMYB9 to MdANS and MdANR. The JA signaling repressor MdJAZ1 interacted with MdTRB1 and interfered with the interaction between MdTRB1 and MdMYB9, therefore negatively modulating MdTRB1‐promoted biosynthesis of anthocyanin and proanthocyanidin.
SUMMARY
Abscisic acid (ABA) induces chlorophyll degradation and leaf senescence; however, the molecular mechanism remains poorly understood, especially in woody plants. In this study, we found that ...MdABI5 plays an essential role in the regulation of ABA‐triggered leaf senescence in Malus domestica (apple). Through yeast screening, three transcription factors, MdBBX22, MdWRKY40 and MdbZIP44, were found to interact directly with MdABI5 in vitro and in vivo. Physiological and biochemical assays showed that MdBBX22 delayed leaf senescence in two pathways. First, MdBBX22 interacted with MdABI5 to inhibit the transcriptional activity of MdABI5 on the chlorophyll catabolic genes MdNYE1 and MdNYC1, thus negatively regulating chlorophyll degradation and leaf senescence. Second, MdBBX22 interacted with MdHY5 to interfere with the transcriptional activation of MdHY5 on MdABI5, thereby inhibiting the expression of MdABI5, which also contributed to the delay of leaf senescence. MdWRKY40 and MdbZIP44 were identified as positive regulators of leaf senescence. They accelerated MdABI5‐promoted leaf senescence through the same regulatory pathways, i.e., interacting with MdABI5 to enhance the transcriptional activity of MdABI5 on MdNYE1 and MdNYC1. Taken together, our results suggest that MdABI5 works with its positive or negative interaction partners to regulate ABA‐mediated leaf senescence in apple, in which it acts as a core regulator. The antagonistic regulation pathways ensure that plants respond to external stresses flexibly and efficiently. Our results provide a concept for further study on the regulation mechanisms of leaf senescence.
Significance Statement
MdBBX22 delays leaf senescence by inhibiting the transcriptional activity of MdABI5 on MdNYE1 and MdNYC1 or by interfering with the transcriptional activation of MdHY5 on MdABI5. MdWRKY40 and MdbZIP44 accelerate MdABI5‐promoted leaf senescence by enhancing the transcriptional activity of MdABI5 on MdNYE1 and MdNYC1.
Iron (Fe) is an essential element for plant growth, development and metabolism. Due to its lack of solubility and low bioavailability in soil, Fe levels are usually far below the optimum amount for ...most plants' growth and development. In apple production, excessive use of nitrogen fertilizer may cause iron chlorosis symptoms in the newly growing leaves, but the regulatory mechanisms underlying this phenomenon are unclear. In this study, low nitrate (NO3−, LN) application alleviated the symptoms of Fe deficiency and promoted lower rhizosphere pH, which was beneficial for root Fe acquisition. At the same time, LN treatment increased citrate and abscisic acid accumulation in roots, which promoted Fe transport from root to shoot and maintained Fe homeostasis. Moreover, qRT‐PCR analysis showed that nitrate application caused differential expression of genes related to Fe uptake and transport, as well as transcriptional regulators. In summary, our data reveal that low nitrate alleviated Fe deficiency through multiple pathways, demonstrating a new option for minimizing Fe deficiency by regulating the balance between nutrients.
In this manuscript, we describe an extensive study of the effects of low nitrate (LN) on iron‐deficiency responses. LN treatment aids rhizosphere acidification and increases citrate and abscisic acid accumulation in the roots, thus promoting Fe acquisition and transport from root to shoot, ultimately alleviating Fe deficiency.
The immune checkpoint molecules are emerged in the evolution to protect the host from self-attacks by activated T cells. However, cancer cells, as a strategy to survive and expand, can hijack these ...molecules and mechanisms to suppress T cell-mediated immune responses. Therefore, an idea of blocking the checkpoint molecules to enhance the anti-tumor activities of the host immune system has been developed and applied to the cancer therapy after discovery of the inhibitory T cell co-receptor, cytotoxic T-lymphocyte associated protein 4 (CTLA-4), and further enhanced on the identification of PD-1 and its ligands. Since 2010, several checkpoint inhibitors have been approved by FDA and many more are in clinical trials. In the treatment of advanced cancers, these inhibitors significantly increased response rates and survival benefits. However, accompanied with the striking results, immune-related adverse events (irAEs) that broadly occurred in many organs were observed and reported, some of which were fatal. Herein, we first review the recent progressions in the research of the immune checkpoint molecules and the application of their blocking antibodies in cancer treatment, and then discuss the cardiac toxicity induced by the therapy and the strategy to monitor, manage this adverse event when it occurs.
Abstract
Nitrate is a major nitrogen resource for plant growth and development and acts as both a crucial nutrient and a signaling molecule for plants; hence, understanding nitrate signaling is ...important for crop production. Abscisic acid (ABA) has been demonstrated to be involved in nitrate signaling, but the underlying mechanism is largely unknown in apple. In this study, we found that exogenous ABA inhibited the transport of nitrate from roots to shoots in apple, and the transcription of the nitrate transporter
MdNRT1.5
/
MdNPF7.3
was noticeably reduced at the transcriptional level by ABA, which inhibited the transport of nitrate from roots to shoots. Then, it was found that the ABA-responsive transcription factor MdABI5 bound directly to the ABRE recognition site of the
MdNRT1.5
promoter and suppressed its expression. Overexpression of
MdABI5
inhibited ABA-mediated transport of nitrate from roots to shoots. Overall, these results demonstrate that MdABI5 regulates the transport of nitrate from roots to shoots partially by mediating the expression of
MdNRT1.5
, illuminating the molecular mechanism by which ABA regulates nitrate transport in apple.
Ubiquitination is an important post-translational protein modification. Although BROAD-COMPLEX, TRAMTRACK AND BRIC A BRAC and TRANSCRIPTION ADAPTOR PUTATIVE ZINC FINGER domain protein 2 (BT2) is ...involved in many biological processes, its role in apple (Malus domestic) root formation remains unclear. Here, we revealed that MdBT2 inhibits adventitious root (AR) formation through interacting with AUXIN RESPONSE FACTOR8 (MdARF8) and INDOLE-3-ACETIC ACID INDUCIBLE3 (MdIAA3). MdBT2 facilitated MdARF8 ubiquitination and degradation through the 26S proteasome pathway and negatively regulated GRETCHEN HAGEN 3.1 (MdGH3.1) and MdGH3.6 expression. MdARF8 regulates AR formation through inducing transcription of MdGH3s (MdGH3.1, MdGH3.2, MdGH3.5, and MdGH3.6). In addition, MdBT2 facilitated MdIAA3 stability and slightly promoted its interaction with MdARF8. MdIAA3 inhibited AR formation by forming heterodimers with MdARF8 as well as other MdARFs (MdARF5, MdARF6, MdARF7, and MdARF19). Our findings reveal that MdBT2 acts as a negative regulator of AR formation in apple.
5-hydroxytryptamine (5-HT) is ubiquitously present in animals and plants, playing a vital regulatory role. SERT, a conserved serotonin reuptake transporter in animals, regulates intracellular and ...extracellular concentrations of 5-HT. Few studies have reported 5-HT transporters in plants. Hence, we cloned MmSERT, a serotonin reuptake transporter, from Mus musculus. Ectopic expression of MmSERT into apple calli, apple roots and Arabidopsis. Because 5-HT plays a momentous role in plant stress tolerance, we used MmSERT transgenic materials for stress treatment. We found that MmSERT transgenic materials, including apple calli, apple roots and Arabidopsis, exhibited a stronger salt tolerance phenotype. The reactive oxygen species (ROS) produced were significantly lower in MmSERT transgenic materials compared with controls under salt stress. Meanwhile, MmSERT induced the expression of SOS1, SOS3, NHX1, LEA5 and LTP1 in response to salt stress. 5-HT is the precursor of melatonin, which regulates plant growth under adversity and effectively scavenges ROS. Detection of MmSERT transgenic apple calli and Arabidopsis revealed higher melatonin levels than controls. Besides, MmSERT decreased the sensitivity of apple calli and Arabidopsis to abscisic acid (ABA). In summary, these results demonstrated that MmSERT plays a vital role in plant stress resistances, which perhaps serves as a reference for the application of transgenic technology to improve crops in the future.
•We cloned the MmSERT, a mouse serotonin reuptake transporter gene, and ectopically expressed it in apple and Arabidopsis.•Melatonin levels were higher in MmSERT transgenic apple calli and Arabidopsis than in controls.•MmSERT not only improved the salt resistance of transgenic plants, but also decreased their sensitivity to ABA.
•MdBT2 is a negative regulator in response to drought stress.•MdNAC143 is a positive regulator in response to drought stress.•MdBT2 interacts with MdNAC143 and promotes its degradation via the 26S ...proteasome pathway.•MdBT2 confers sensitivity to drought at least dependent on MdNAC143.
Drought stress is a severe source of abiotic stress that can affect apple yield and quality, yet the underlying molecular mechanism of the drought stress response and the role of MdBT2 in the process remain unclear. Here, we find that MdBT2 negatively regulates the drought stress response. Both in vivo and in vitro assays indicated that MdBT2 interacted physically with and ubiquitinated MdNAC143, a member of the NAC TF family that is a positive regulator under drought stress. In addition, MdBT2 promotes the degradation of MdNAC143 via the 26S proteasome system. A series of transgenic assays in apple calli and Arabidopsis verify that MdBT2 confers susceptibility to drought stress at least in part by the regulation of MdNAC143. Overall, our findings provide new insight into the mechanism of MdBT2, which functions antagonistically to MdNAC143 in regulating drought stress by regulating the potential downstream target protein MdNAC143 for proteasomal degradation in apple.
Key message
Ectopic expression of
MmCYP1A1
gene from
Mus musculus
in apple calli and
Arabidopsis
increased the levels of melatonin and 6-hydroxymelatonin, and improved their stress resistance.
...Melatonin occurs widely in organisms, playing a key regulatory role. CYP1A1 is a cytochrome P450 monooxygenase, involved in the melatonin metabolism, and is responsible for the synthesis of 6-hydroxymelatonin from melatonin. Melatonin and 6-hydroxymelatonin have strong antioxidant activities in animals. Here, we cloned
MmCYP1A1
from
Mus musculus
and found that ectopic expression of
MmCYP1A1
improved the levels of melatonin and 6-hydroxymelatonin in transgenic apple calli and
Arabidopsis
. Subsequently, we observed that
MmCYP1A1
increased the tolerance of transgenic apple calli and
Arabidopsis
to osmotic stress simulated by polyethylene glycol 6000 (PEG 6000), as well as resistance of transgenic
Arabidopsis
to drought stress. Further, the number of lateral roots of
MmCYP1A1
transgenic
Arabidopsis
were enhanced significantly after PEG 6000 treatment. The expression of
MmCYP1A1
remarkably reduced malondialdehyde (MDA) content, electrolyte leakage, accumulation of H
2
O
2
and O
2
−
during stress treatment. Moreover,
MmCYP1A1
enhanced stress tolerance in apple calli and
Arabidopsis
by increasing the expression levels of resistance genes.
MmCYP1A1
also promoted stomatal closure in transgenic
Arabidopsis
to reduce leaf water loss during drought. Our results indicate that
MmCYP1A1
plays a key role in plant stress tolerance, which may provide a reference for future plant stress tolerance studies.
•Low Pi conditions alleviate Fe deficiency in apples.•FCR activation and proton extrusion is effective way to alleviate Fe deficiency under low Pi conditions.•Low Pi conditions promote Fe ...accumulation.•Low Pi conditions are involved in organic acid-mediated Fe deficiency.
The accumulation of iron (Fe) in the apical meristem is considered as a critical factor involved in limiting the elongation of roots under low phosphate (Pi) conditions. Furthermore, the antagonism between Fe and Pi largely affects the effective utilization of Fe. Although the lack of Pi serves to increase the effectiveness of Fe in rice under both Fe-sufficient and Fe-deficient conditions, the underlying physiological mechanism governing this phenomenon is still unclear. In this study, we found that low Pi alleviated the Fe-deficiency phenotype in apples. Additionally, low Pi treatments increased ferric-chelated reductase (FCR) activity in the rhizosphere, promoted proton exocytosis, and enhanced the Fe concentration in both the roots and shoots. In contrast, high Pi treatments inhibited this process. Under conditions of low Pi, malate and citrate exudation from apple roots occurred under both Fe-sufficient and Fe-deficient conditions. In addition, treatment with 0.5 mM malate and citrate effectively alleviated the Fe and Pi deficiencies. Taken together, these data support the conclusion that a low Pi supply promotes organic acids exudation and enhances Fe absorption during Fe deficiency in apples.
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