Banana wilt disease, caused by the fungal pathogen Fusarium oxysporum f. sp. cubense 4 (Foc4), is regarded as one of the most devastating diseases worldwide. Cavendish cultivar ‘Yueyoukang 1’ was shown to have significantly lower disease severity and incidence compared with susceptible cultivar ‘Brazilian’ in greenhouse and field trials. De novo sequencing technology was previously performed to investigate defense mechanism in middle resistant ‘Nongke No 1’ banana, but not in highly resistant cultivar ‘Yueyoukang 1’. To gain more insights into the resistance mechanism in banana against Foc4, Illumina Solexa sequencing technology was utilized to perform transcriptome sequencing of ‘Yueyoukang 1’ and ‘Brazilian’ and characterize gene expression profile changes in the both two cultivars at days 0.5, 1, 3, 5 and 10 after infection with Foc4. The results showed that more massive transcriptional reprogramming occurs due to Foc4 treatment in ‘Yueyoukang 1’ than ‘Brazilian’, especially at the first three time points, which suggested that ‘Yueyoukang 1’ had much faster defense response against Foc4 infection than ‘Brazilian’. Expression patterns of genes involved in ‘Plant-pathogen interaction’ and ‘Plant hormone signal transduction’ pathways were analyzed and compared between the two cultivars. Defense genes associated with CEBiP, BAK1, NB-LRR proteins, PR proteins, transcription factor and cell wall lignification were expressed stronger in ‘Yueyoukang 1’ than ‘Brazilian’, indicating that these genes play important roles in banana against Foc4 infection. However, genes related to hypersensitive reaction (HR) and senescence were up-regulated in ‘Brazilian’ but down-regulated in ‘Yueyoukang 1’, which suggested that HR and senescence may contribute to Foc4 infection. In addition, the resistance mechanism in highly resistant ‘Yueyoukang 1’ was found to differ from that in middle resistant ‘Nongke No 1’ banana. These results explain the resistance in the highly resistant cultivar and provide more insights in understanding the compatible and incompatible interactions between banana and Foc4.

Background: Plant genomes contain a large number of HAK/KUP/KT transporters, which play important roles in potassium uptake and translocation, osmotic potential regulation, salt tolerance, root morphogenesis and plant development. Potassium deficiency in the soil of a sugarcane planting area is serious. However, the HAK/KUP/KT gene family remains to be characterized in sugarcane (Saccharum). Results: In this study, 30 HAK/KUP/KT genes were identified in Saccharum spontaneum. Phylogenetics, duplication events, gene structures and expression patterns were analyzed. Phylogenetic analysis of the HAK/KUP/KT genes from 15 representative plants showed that this gene family is divided into four groups (clades I-IV). Both ancient wholegenome duplication (WGD) and recent gene duplication contributed to the expansion of the HAK/KUP/KT gene family. Nonsynonymous to synonymous substitution ratio (Ka/Ks) analysis showed that purifying selection was the main force driving the evolution of HAK/KUP/KT genes. The divergence time of the HAK/KUP/KT gene family was estimated to range from 134.8 to 233.7 Mya based on Ks analysis, suggesting that it is an ancient gene family in plants. Gene structure analysis showed that the HAK/KUP/KT genes were accompanied by intron gain/loss in the process of evolution. RNA-seq data analysis demonstrated that the HAK/KUP/KT genes from clades II and III were mainly constitutively expressed in various tissues, while most genes from clades I and IV had no or very low expression in the tested tissues at different developmental stages. The expression of SsHAK1 and SsHAK21 was upregulated in response to low-K + stress. Yeast functional complementation analysis revealed that SsHAK1 and SsHAK21 could rescue K + uptake in a yeast mutant. Conclusions: This study provided insights into the evolutionary history of HAK/KUP/KT genes. HAK7/9/18 were mainly expressed in the upper photosynthetic zone and mature zone of the stem. HAK7/9/18/25 were regulated by sunlight. SsHAK1 and SsHAK21 played important roles in mediating potassium acquisition under limited K + supply. Our results provide valuable information and key candidate genes for further studies on the function of HAK/KUP/KT genes in Saccharum.

To understand dynamic changes in rhizosphere microbial community in consecutive monoculture, Illumina MiSeq sequencing was performed to evaluate the V3-V4 region of 16S rRNA in the rhizosphere of newly planted and three-year ratooning sugarcane and to analyze the rhizosphere bacterial communities. A total of 126,581 and 119,914 valid sequences were obtained from newly planted and ratooning sugarcane and annotated with 4445 and 4620 operational taxonomic units (OTUs), respectively. Increased bacterial community abundance was found in the rhizosphere of ratooning sugarcane when compared with the newly planted sugarcane. The dominant bacterial taxa phyla were similar in both sugarcane groups. Proteobacteria accounted for more than 40% of the total bacterial community, followed by Acidobacteria and Actinobacteria. The abundance of Actinobacteria was higher in the newly planted sugarcane, whereas the abundance of Acidobacteria was higher in the ratooning sugarcane. Our study showed that Sphingomonas, Bradyrhizobium, Bryobacter, and Gemmatimonas were dominant genera. Moreover, the richness and diversity of the rhizosphere bacterial communities slightly increased and the abundance of beneficial microbes, such as Bacillus, Pseudomonas, and Streptacidiphilus, in ratooning sugarcane were more enriched. With the consecutive monoculture of sugarcane, the relative abundance of functional groups related to energy metabolism, glycan biosynthesis, metabolism, and transcription were overrepresented in ratooning sugarcane. These findings could provide the way for promoting the ratooning ability of sugarcane by improving the soil bacterial community.

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In 2006, the release and cultivation of the genetically modified papaya cultivar ‘Huanong No.1’ successfully controlled the destructive papaya ringspot disease caused by Papaya ringspot virus (PRSV) in South China. However, some transgenic papaya plants from Guangdong and Hainan are found infected by PRSV. In this study, Field investigation was carried out and susceptible transgenic papaya samples were collected during 2012–2016. Twenty representative isolates were artificially inoculated into Cucurbita pepo and commercialised ‘Huanong No.1’ papaya, and results indicated that the plants showed obvious disease symptoms. Phylogenetic analysis of CP genes of 120 PRSV-infected isolates showed that PRSV can be divided into three groups. Isolates from Guangdong and Hainan belong to Group III, which is further divided into two subgroups. The isolates collected in this study have greatly diverged from the previously reported dominant strains Ys, Vb and Sm in South China, indicating that they belong to a new lineage. Further analysis showed a highly genetic differentiation between isolates, and 27.1% of the isolates were identified as recombinants on the basis of CP nucleotide sequences. These results indicate that the genetic variation of PRSV and the formation of the new virus lineage may explain the loss of transgenic papaya resistance in South China.