How the PA, ABA and CBF pathways are synergistic

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Polyamines (PAs), including putrescine (Put, a diamine), spermidine (Spd, a triamine) and spermine (Spm, a tetramine), are low molecular weight polycations and aliphatic nitrogenous substances. They play an important role in the overall life cycle of plants, from seed germination to fruit maturation, abscission and senescence. There has been an increasing interest in studying PAs involved in plant stresses including drought, hypoxia, high temperature, low temperature, salinity and metal toxicity. The primary role of PAs in plant stress is to thwart reactive oxygen species (ROS) damage and prevent free radical damage or oxidative stress while modulating ion channels to protect morphology and the integrity of cell membranes, nucleic acids and proteins. . PAs interact with hormonal pathways (ethylene, jasmonate, auxin, gibberellins, cytokinins, abscisic acid) [ABA]salicylic acid and brassinosteroids) and other signaling molecules (Ca2+NO, H2O2and gamma-aminobutyric acid) to help plants cope with adverse environments.

Over the past two decades, there has been an emerging understanding of crosstalk between ABA and PAs in response to environmental stress. ABA-responsive element binding factors (ABFs) (ABFs) are essential components of ABA signaling and are widely implicated in plant growth and development, as well as responses to biotic and abiotic stresses such as cold. C-repeat binding factors (CBFs) act at the crossroads of the transcriptional regulatory network that underlies the cold stress response. They can bind directly to DRE/CRT (Dehydration Reactive Element/C-Repeat) cis-acting on the promoters of cold-regulated genes (COR) and triggering their expression to help plants resist biting cold.

The melon, which is native to tropical and subtropical regions but is now grown worldwide, is vulnerable to cold damage in temperate latitudes. Evidence suggests that exogenous ABA can improve cold tolerance of oriental melon seedlings, and PA accumulation contributes to adaptation to root zone hypoxia stress, Ca(NO3)2 stress and salinity-alkalinity stress in melon seedlings, as well as cold stress in melon fruits. Only two CmCBFs, CmCBF1 and CmCBF3, have been identified and their expression is positively correlated with cold tolerance in melon. However, whether the PA, ABA, and CBF pathways synergistically regulate cold tolerance in melon is largely unknown.

Recently, scientists from Shenyang Agricultural University reported that ABA, CBF and polyamine pathways could form a cooperative regulatory network to control plant response to cold stress. In a preliminary experiment, the authors found that among the three PAs, only Put was present at significantly higher levels in a cold-tolerant genotype compared to a cold-sensitive genotype. Since arginine decarboxylase (ADC) is the key synthetase that catalyzes the biosynthesis of putrescine in plants, the authors then examined the expression of the gene encoding ADC. CmADC under cold treatment. As expected, the low temperatures induced CmADC expression and sequence analysis showed that the CmADC the promoter contained at least three ABRE motifs and three DRE motifs. The authors isolated four CmCBF and five CmABF which were significantly induced in response to cold stress. CmABF1 and CmCBF4 were selected as candidate TFs that could bind directly to promoter fragments of CmADC in vitro and in plant promote its transcription. Virus-induced gene silencing (VIGS) assays have further demonstrated that CmABF1 and CmCBF4 played a positive role in the cold tolerance of melon seedlings by promoting the synthesis of Put. This work was published in the journal Horticultural research.

“Our study provides new evidence that the ABA and CBF pathways in the cold response are not entirely independent and that CmADC is at the junction of these pathways,” the researchers said.

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Reference

Authors

Meng Li 1,2,3Xiaoyu Duan 1,2,3Ge Gao 1,2,3Tao Liu 1,2,3 and Hongyan Qi 1,2,3

Memberships

1 College of Horticulture, Shenyang Agricultural University, Shenyang 110866, Liaoning, China

2 Key Laboratory of Protected Horticulture of Education Ministry and Liaoning Province, Shenyang 110866, Liaoning, China

3 National and Local Joint Engineering Research Center of Northern Horticultural, Facilities Design and Application Technology (Liaoning), Shenyang 110866, Liaoning, China

About Dr. Hongyan Qi

Dr. Hongyan Qi is a professor at the College of Horticulture, Shenyang Agricultural University. It contributes to studies on the physiological and molecular mechanisms by which the melon adapts to cold stress. She is also interested in fruit quality formation and regulation of watermelon and melon.

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