Transcriptional Effects of Rootstock on Scion after Drought: A Case Study of Using <i>MdGH3</i> RNAi as the Rootstock

Drought stress is an important environmental factor limiting apple yield and fruit quality. Previously, we identified GRETCHEN HAGEN3.6 (GH3.6) as a negative regulator of drought stress in apple trees. Using transgenic MdGH3 RNAi (knocking down MdGH3.6 and its five homologs) plants as rootstock can increase drought tolerance, water use efficiency, flowering, and fruit quality of the Fuji scion after drought stress. However, the molecular mechanism behind this phenomenon is still unknown. Here, we performed transcriptome sequencing of the grafted plants (Fuji/GL-3 where Fuji was used as the scion and non-transgenic GL-3 was used as the rootstock, and Fuji/MdGH3 RNAi where MdGH3 RNAi was used as the rootstock) under control and drought conditions. Under control conditions, 667 up-regulated genes and 176 down-regulated genes were identified in the scion of Fuji/MdGH3 RNAi, as compared to the scion of Fuji/GL-3. Moreover, 941 up-regulated genes and 2226 down-regulated genes were identified in the rootstock of MdGH3 RNAi plants relative to GL-3. GO terms of these differentially expressed genes (DEGs) in scion and rootstock showed associations with plant growth, fruit development, and stress responses. After drought stress, 220 up-regulated and 452 down-regulated genes were identified in MdGH3 RNAi rootstock, as compared to GL-3. Significantly enriched GO terms included response to abiotic stimulus, cell division, microtubule-based process, metabolic and biosynthetic process of flavonoid, pigment, and lignin. The comparison between the scion of Fuji/MdGH3 RNAi and Fuji/GL-3 yielded a smaller number of DEGs; however, all of them were significantly enriched in stress-related GO terms. Furthermore, 365 and 300 mRNAs could potentially move from MdGH3 RNAi rootstock to scion under control and drought conditions, respectively, including FIDDLEHEAD (FDH), RESPONSIVE TO DESICCATION 26 (RD26), ARS-binding factor 2 (ABF2), WRKY75, and ferritin (FER). Overall, our work demonstrates the effects of rootstock on scion at the transcriptional level after drought stress and provides theoretical support for further understanding and utilization of MdGH3 RNAi plants

Interfering small ubiquitin modifiers (SUMO) exhibits apple's enhanced tolerance to nitrogen deficiency

Nitrogen is one of the most critical macroelements required for apple biomass accumulation and quality formation. Thus, identification and characterization of candidate genes involved in nitrogen deficiency stress is of great importance to the sustainable development of the apple industry. SUMOylation is a kind of post-translational modification, which is widely involved in plant life processes, including responses to nitrogen (N) deficiency. Here, we identified apple small ubiquitin modifiers (SUMO) that participated in responding to nitrogen deficiency. Firstly, all isoforms of apple SUMOs were induced by N deficiency stress. Under N deficiency stress conditions, the MdSUMO2 RNAi transgenic apple plants showed better growth potential than the wild type GL-3, including more new leaves, increased height, thicker stems, and heavier fresh weight. In addition, the MdSUMO2 RNAi transgenic apple plants exhibited darker green leaves and greater root volume than GL-3 in response to N deficient conditions. Finally, the activated glutamine synthetase (GS) activity, nitrate reductase (NR) activity, as well as the induced expression of genes involved in nitrogen assimilation in the root might contribute to the tolerance of MdSUMO2 RNAi transgenic apple plants in response to nitrogen deficiency. Taken together, our finding provides insight to further study the mechanisms underlying the essential roles of apple MdSUMOs in responding to N deficient conditions

Interfering small ubiquitin modifiers (SUMO) improves the thermotolerance of apple by facilitating the activity of MdDREB2A

Abstract Heat stress, which is caused by global warming, threatens crops yield and quality across the world. As a kind of post-translation modification, SUMOylation involves in plants heat stress response with a rapid and wide pattern. Here, we identified small ubiquitin modifiers (SUMO), which affect drought tolerance in apple, also participated in thermotolerance. Six isoforms of SUMOs located on six chromosomes in apple genome, and all the SUMOs were up-regulated in response to heat stress condition. The MdSUMO2 RNAi transgenic apple plants exhibited higher survival rate, lower ion leakage, higher catalase (CAT) activity, and Malondialdehyde (MDA) content under heat stress. MdDREB2A, the substrate of MdSUMO2 in apple, was accumulated in MdSUMO2 RNAi transgenic plants than the wild type GL-3 at the protein level in response to heat stress treatment. Further, the inhibited SUMOylation level of MdDREB2A in MdSUMO2 RNAi plants might repress its ubiquitination, too. The accumulated MdDREB2A in MdSUMO2 RNAi plants further induced heat-responsive genes expression to strengthen plants thermotolerance, including MdHSFA3, MdHSP26.5, MdHSP18.2, MdHSP70, MdCYP18-1 and MdTLP1. In summary, these findings illustrate that interfering small ubiquitin modifiers (SUMO) in apple improves plants thermotolerance, partly by facilitating the stability and activity of MdDREB2A

An atypical R2R3 MYB transcription factor increases cold hardiness by CBF-dependent and CBF-independent pathways in apple

Apple (Malus × domestica) trees are vulnerable to freezing temperatures. However, there has been only limited success in developing cold-hardy cultivars. This lack of progress is due at least partly to lack of understanding of the molecular mechanisms of freezing tolerance in apple. In this study, we evaluated the potential roles for two R2R3 MYB transcription factors (TFs), MYB88 and the paralogous FLP (MYB124), in cold stress in apple and Arabidopsis. We found that MYB88 and MYB124 positively regulate freezing tolerance and cold-responsive gene expression in both apple and Arabidopsis. Chromatin-Immunoprecipitation-qPCR and electrophoretic mobility shift assays showed that MdMYB88/MdMYB124 act as direct regulators of the COLD SHOCK DOMAIN PROTEIN 3 (MdCSP3) and CIRCADIAN CLOCK ASSOCIATED 1 (MdCCA1) genes. Dual luciferase reporter assay indicated that MdCCA1 but not MdCSP3 activated the expression of MdCBF3 under cold stress. Moreover, MdMYB88 and MdMYB124 promoted anthocyanin accumulation and H2O2 detoxification in response to cold. Taken together, our results suggest that MdMYB88 and MdMYB124 positively regulate cold hardiness and cold-responsive gene expression under cold stress by C-REPEAT BINDING FACTOR (CBF)-dependent and CBF-independent pathways

A chromosome-scale reference genome provides insights into the genetic origin and grafting-mediated stress tolerance of Malus prunifolia

27openInternationalInternational coauthor/editoropenLi, Z.; Wang, L.; He, J.; Li, X.; Hou, N.; Guo, J.; Niu, C.; Li, C.; Liu, S.; Xu, J.; Xie, Y.; Zhang, D.; Shen, X.; Lu, L.; Gend, D.; Chen, P.; Jiang, L.; Wang, L.; Li, H.; Malnoy, M.; Deng, C.; Zou, Y.; Li, C.; Zhan, X.; Ma, F.; Zu, Q.; Guan, Q.Li, M.; Wang, L.; He, J.; Li, X.; Hou, N.; Guo, J.; Niu, C.; Li, C.; Liu, S.; Xu, J.; Xie, Y.; Zhang, D.; Shen, X.; Lu, L.; Gend, D.; Chen, P.; Jiang, L.; Wang, L.; Li, H.; Malnoy, M.; Deng, C.; Zou, Y.; Li, C.; Zhan, X.; Ma, F.; Zu, Q.; Guan, Q