Highlights d Tuber formation is dependent on the link between photoperiod and sugar transport d Potato FT-like tuberigen interacts with a sugar transporter to block sucrose leakage d StSWEET11-StSP6A interaction promotes symplastic transport of sucrose Authors Jos e A

Dry rot is a serious potato disease and causes significant losses in China. Research efforts on potato dry rot have been very limited as well as the attempts to characterize the pathogen in the major potato production regions of China. A total of 260 Fusarium isolates were identified in 698 potato tubers collected in six important potato production regions of northern China, out of which five different Fusarium species, Fusarium sambucinum, F. avenaceum, F. oxysporum, F. equiseti, and F. acuminatum, were isolated. The identification of each species was confirmed by sequencing analysis of ∼700 bp DNA fragment derived from the translation elongation factor-1 alpha gene. F. sambucinum was found to be the predominant species accounting for 56% of the isolates. Different pathogenicity was found to be associated with five most common Fusarium species. Sixty-seven clones used in China were identified as susceptible to F. sambucinum, indicating little scope for developing resistant cultivars using the currently available potato germplasm.

These authors contributed equally. SUMMARYOver 200 imprinted genes in rice endosperm are known, but the mechanisms modulating their parental allele-specific expression are poorly understood. Here we use three imprinted genes, OsYUCCA11, yellow2-like and ubiquitin hydrolase, to show that differential DNA methylation and tri-methylation of histone H3 lysine 27 (H3K27me 3 ) in the promoter and/or gene body influences allele-specific expression or the site of transcript initiation. Paternal expression of OsYUCCA11 required DNA methylation in the gene body whereas the gene body of the silenced maternal allele was hypomethylated and marked with H3K27me 3 . These differential markings mirror those proposed to modulate paternal expression of two Arabidopsis genes, PHERES1 and a YUCCA homolog, indicating conservation of imprinting mechanisms. At yellow2-like, DNA hypomethylation in the upstream flanking region resulted in maternal transcripts that were longer than paternal transcripts; the maternal transcript initiation site was marked by DNA methylation in the paternal allele, and transcription initiated~700 bp downstream. The paternal allele of an ubiquitin hydrolase gene exhibited gene body DNA methylation and produced full-length transcripts, while the maternal allele was hypomethylated in the 5 0 gene body and transcripts initiated from a downstream promoter. Inhibition of DNA methylation by 5-azacytidine or zebularine activated the long transcripts from yellow2-like and enhanced expression of the short transcripts from the ubiquitin hydrolase in seedlings, indicating that DNA methylation prevents transcript initiation from cryptic promoters. These observations suggest a paradigm whereby maternal genome hypomethylation is associated with the production of distinct transcripts, potentially diversifying the gene products from the two alleles.

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