Mechanism On The Graft Compatibility Between ‘Jingganghongnuo’ And Other Litchi Cultivars

Grafting is the stock and scion healing process and can make different organ combine into an organic.Grafting healing processis complicated,whichinvoloes histology and cytology problems.Scholars from different aspects(morphology,anatomy, physiology, biochemical and genetic) to deeply explore the mechanism.In this study, ‘Jingganghongnuo’, a new litchi cultivar, was grafted on the rootstock of cultivar, We analyzed the grafting compatibility between ‘Jingganghongnuo’ and other litchi cultivars and measured many physiological and biochemical indexes. we hoped find a correlation between them.We observed anatomical differences among combinations by paraffin section, Finally, comparative transcriptomic analysis was performed with different level of compatible combinations, to gain further understanding of the molecular mechanisms involved in graft compatibility in litchi. The main results are as follows:1 In this study, ‘Jingganghongnuo’, a new litchi cultivar, was grafted on the rootstock of cultivar‘Jingfeng’, ‘Heiye’, ‘Huaizhi’, ‘Songjiaxiang’, ‘Guilin’, ‘Xuehuaizi’, ‘Zhuangyuanhong’, ‘Liuyuexue’, ‘Baitangying’, ‘Wuye’, ‘Shuangjianyuhebao’, ‘Wanpu’, ‘Zaopu’ to determine their compatibility. The survivalrate was determined 6 months after grafting. Significant difference in chlorophyll contents was detectedbetween compatible combinations and incompatible combinations 6 months after grafting. We found ‘Jingganghongnuo/Liuyuexue’,‘Jingganghongnuo/Baitangying’ and ‘Jingganghongnuo/Huaizhi’ were compatible combinations. Compatiblecombinations showed dark green leaf and smooth graft joint, while, the incompatible ones had yellowleaf. In addition, the compatible combinations had higher SOD, POD and PPO activities than that inthe incompatible ones.2 In addition, we analyzed 14 litchicultivars genetic relationship by flow cytometry and SCo T molecular marker,We found that higher compatible rates of graft combinations, the closer relationship among the litchi cultivars. We also measured many physiological and biochemical indexes, We found dry weight, leaf and soluble sugar content significantly associated with graft compatibility. So we can predict the graft compatibility by measuring the above indexes.We observed anatomical differences among combinations by paraffin section, Histological assay indicated that the compatible combinations developed vascular bundle bridgefrom the wound tissues, while, there was few vascular bundle bridge connected in incompatible combinations.3 Abundance analysis identified 6,060 DEGs were significant expression in the compatible combinations and 5,267 DEGs exhibiting in the incompatibility. We also found many transcription factors, such as MYB, WRKY and NAC. KEGG pathway enrichment analysis revealed that DEGs exhibiting differential expression were involved in the metabolism and signal transduction of various phytohormones. The expression levels of DEGs of annotated as auxin were up-regulated in compatible combinations at the early stage. However, we could not find up-regulated in incompatible cominations.Biological analysis of samples were indicated the IAA can influence the grafting process. In addition, 16 DEGs exhibiting sequence similarities to known ligin-related genes from other plants were differentially expressed during graft healing process.4 Three key candidate genes related to litchi lignin synthesis, Lc PODandLc PAL were further studied about their sequences, expression pattern and function. Phylogenetic analysis revealed that, Lc PODwas close to Pt POD, Lc PAL1 and Cit PAL(81.98%), Lc PAL2 and Cs PAL(77.02%) were highly homolog, Q-PCR analysis indicated that Lc POD and Lc PAL were expressed in both combinations, but they were expressed higer in the compatibility combination. The Lc POD and Lc PALtransgenic tobacco had higher content than non-transgenic tobacco. By transgenic tobacco grafting experiments,we found Lc PAL1-line2/CK and CK/ Lc PAL1-line2 had well growth vigor, followed Lc PAL2-line2/CK and CK/Lc PAL2-line2, their PAL activity were significantly higher than WT. And Lc POD1-line1/CK and CK/Lc POD1-line1 had the worst growth vigor. The localization and functional identification Lc MYB showed that they both were nuclear localization, and they can regulate the Lc PALand Lc C3 H.