Phosphorylated transcription factor PuHB40 mediates ROS-dependent anthocyanin biosynthesis in pear exposed to high light

Phosphorylation of MdWRKY70L by MdMPK6/02G mediates reactive oxygen accumulation to regulate apple fruit senescence

Apple (Malus domestica Borkh.) is a globally significant crop and a vital dietary component worldwide. During ripening, apples exhibit a longitudinal gradient, ripening first at the stalk cavity and extending towards the calyx concave. When the fruit is harvested at the right time or later, the stalk cavity of many varieties often shows over-ripening, that is, premature senescence such as peel browning, which diminishes fruit quality. This study examines the natural senescence process in 6-year-old 'Ruixue' apples by screening transcriptome data to uncover senescence-related genes and validate their molecular functions. Our analysis of antioxidant capacity and reactive oxygen species (ROS) in different peel regions revealed that malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O 2 - ⋅ ) levels increased with senescence, where ROS-scavenging enzyme activity was notably reduced, especially in the stalk cavity (compared with the fruits in the stalk cavity at 120 days, the activities of SOD, POD, and CAT in stalk cavity of fruits at 205 days were significantly decreased in 65.4%, 82.7%, and 91.1%, respectively). Transcriptome clustering and enrichment analyses across developmental stages revealed MdWRKY70L, MdSAG101, and MdZAT12 as key regulators of peel senescence. MdWRKY70L could interact with MdSAG101/MdZAT12 both in vivo and in vitro, thereby mediating ROS accumulation in the peel and accelerating the fruit senescence process. Further in vitro and in vivo studies demonstrated that MdWRKY70L is phosphorylated at Ser199 by MdMPK6/02G, enhancing MdWRKY70L protein stability and promoting peel senescence. These findings offer insights for developing strategies to delay fruit senescence and improve postharvest quality control.

The MdHB7L-MdICE1L-MdHOS1 Module Fine-Tunes Apple Cold Response via CBF-Dependent and CBF-Independent Pathways

Cold stress is a major environmental factor limiting crop yield, quality, and geographical distribution worldwide. The homeodomain-leucine zipper (HD-Zip) transcription factor (TF) family plays a role in regulating plant abiotic stress responses, but the underlying mechanisms remain unclear. A HD-Zip TF, MdHB7L, is identified as promoting cold tolerance in apple. MdHB7L interacts with MdICE1L, enhancing its transcriptional activation of MdCBFs, and directly binds to MdCBF promoters to activate their expression. Conversely, MdICE1L inhibits the direct binding of MdHB7L on MdCBF promoters, revealing that MdHB7L acts as a cofactor rather than a TF when interacting with MdICE1L. Using ChIP-seq and RNA-seq, MdHB7L is found to directly regulate the expression of several key genes involved in ROS scavenging and biosynthesis of anthocyanins, soluble sugars, and proline, thereby enhancing apple cold tolerance. The E3 ubiquitin ligase MdHOS1 negatively regulates cold tolerance by interacting with and mediating the degradation of MdHB7L and MdICE1L, with a preference for MdICE1L over MdHB7L. This preference inhibits the MdHOS1-MdHB7L interaction and stabilizes MdHB7L, allowing it to sustain the plant's cold response as a TF after MdICE1L degradation. These findings provide new insights into the dynamic plant response to cold stress mediated by the MdHB7L-MdICE1-MdHOS1 module.

Cloning and Functional Analysis of ZFP5 from Amorpha fruticosa for Enhancing Drought and Saline-Alkali Resistance in Tobacco

Drought and soil salinization significantly constrain agricultural productivity, driving the need for molecular breeding strategies to enhance stress resistance. Zinc finger proteins play a critical role in plant response to abiotic stress. In this study, a gene encoding a C2H2-type zinc finger protein (AfZFP5) was cloned from Amorpha fruticosa, a species known for its strong adaptability. qRT-PCR analysis revealed that AfZFP5 expression is regulated by sorbitol, H2O2, NaCl, and NaHCO3. And all four treatments can cause upregulation of AFZFP5 expression in the roots or leaves of Amorpha fruticosa within 48 h. Transgenic tobacco lines overexpressing AfZFP5 demonstrated enhanced tolerance to drought and salt-alkali stress at germination, seedling, and vegetative stages. Compared to wild-type plants, transgenic lines exhibited significantly higher germination rates, root lengths, and fresh weights when treated with sorbitol, NaCl, and NaHCO3. Under natural drought and salt-alkali stress conditions, transgenic plants showed elevated activities of superoxide dismutase (SOD) and peroxidase (POD), and upregulated expression of oxidative stress-related kinase genes (NtSOD, NtPOD) during the vegetative stage. Additionally, transgenic tobacco displayed lower malondialdehyde (MDA) content and reduced staining levels with 3,3'diaminobenzidine (DAB) and Nitro blue tetrazolium (NBT), indicating enhanced reactive oxygen species (ROS) scavenging capacity by AfZFP5 upon salt-alkali stress. Under simulated drought with PEG6000 and salt-alkali stress, chlorophyll fluorescence intensity and Fv/Fm values in transgenic tobacco were significantly higher than in wild-type plants during the vegetative stage, suggesting that AfZFP5 mitigates stress-induced damage to the photosynthetic system. This study highlights the role of AfZFP5 in conferring drought and salt-alkali stress tolerance, providing genetic resources and a theoretical foundation for breeding stress-resistance crops.

Flavonoids as key players in cold tolerance: molecular insights and applications in horticultural crops

Cold stress profoundly affects the growth, development, and productivity of horticultural crops. Among the diverse strategies plants employ to mitigate the adverse effects of cold stress, flavonoids have emerged as pivotal components in enhancing plant resilience. This review was written to systematically highlight the critical role of flavonoids in plant cold tolerance, aiming to address the increasing need for sustainable horticultural practices under climate stress. We provide a comprehensive overview of the role of flavonoids in the cold tolerance of horticultural crops, emphasizing their biosynthesis pathways, molecular mechanisms, and regulatory aspects under cold stress conditions. We discuss how flavonoids act as antioxidants, scavenging reactive oxygen species (ROS) generated during cold stress, and how they regulate gene expression by modulating stress-responsive genes and pathways. Additionally, we explore the application of flavonoids in enhancing cold tolerance through genetic engineering and breeding strategies, offering insights into practical interventions for improving crop resilience. Despite significant advances, a research gap remains in understanding the precise molecular mechanisms by which specific flavonoids confer cold resistance, especially across different crop species. By addressing current knowledge gaps, proposing future research directions and highlighting implications for sustainable horticulture, we aim to advance strategies to enhance cold tolerance in horticultural crops.

GHCYP706A7 governs anthocyanin biosynthesis to mitigate ROS under alkali stress in cotton

KEY MESSAGE

Flavonoid 3'-hydroxylase synthesis gene-GHCYP706A7, enhanced cotton resistance to alkali stress by scavenging ROS to regulate anthocyanin synthesis. Anthocyanins are a class of flavonoids that play a significant role in mediating plant responses to adverse environmental conditions. Flavonoid 3'-hydroxylase (F3'H), a member of the cytochrome P-450 (CYP) family, is a pivotal enzyme involved in the biosynthesis of anthocyanins. The present study identified 398 CYPs in the Gossypium hirsutum genome, of which GHCYP706A7 was responsible for F3'H synthesis and its ability to respond to alkaline stress. GHCYP706A7 suppression through virus-induced gene silencing (VIGS) diminished tolerance to alkali stress in cotton, evidenced by significantly reduced anthocyanin synthesis, markedly decreased antioxidant capacity, notable increases in reactive oxygen species, severe cellular damage, and observably decreased stomatal opening. The cumulative effects of these physiological disruptions ultimately manifest in cotton wilting and fresh weight decline. These findings lay a foundation for further investigations into the role of CYPs in regulating anthocyanin synthesis and responding to alkali stress.

PKS1 involved in anthocyanin accumulation in red-skinned pear fruit

KEY MESSAGE

PcPKS1 can prevent PcCSN5a from acting as an inhibitor of anthocyanin synthesis by binding to PcCSN5a, ultimately leading the accumulation of anthocyanins. Light is a crucial environmental factor that regulates anthocyanin accumulation in plants. However, the molecular mechanisms by which light signals influence anthocyanin accumulation in fruits have not yet been fully elucidated. We identified the differentially expressed gene Pyrus communis PHYTOCHROME KINASE SUBSTRATE 1 (PcPKS1), which is associated with anthocyanin accumulation in plants, in a previous study. Through measurements of the expression of PcPKS1 in 'Starkrimson' and 'Red Bartlett' pear fruit at various developmental stages and in different pear varieties, quantitative and transient expression experiments conducted on red and green skin tissues confirmed the relationship between PcPKS1 and anthocyanin accumulation. Pyrus communis COP9 SIGNALOSOME COMPLEX SUBUNIT 5A (PcCSN5a) protein, which interacts with PcPKS1, was identified from a yeast library screening. The interaction between the two proteins was validated through yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BiFC), and split-luciferase (Split-LUC) experiments. Subcellular localization and co-localization experiments revealed that PcPKS1 was localized to the cell membrane, whereas PcCSN5a was localized to the cell membrane and nucleus, with PcPKS1 and PcCSN5a co-localized on the cell membrane. Transient expression in strawberry fruit indicated that PcPKS1 positively regulated anthocyanin accumulation, whereas PcCSN5a negatively regulated anthocyanin accumulation and diminished the capacity of PcPKS1 to promote anthocyanin accumulation. This study provides novel insights into the molecular mechanisms underlying light-regulated anthocyanin accumulation in red-skinned pear fruit.