Comparative transcriptome analysis reveals key genes and pathways in response to Alternaria alternata apple pathotype infection

Apple leaf spot,caused by the Alternaria alternata apple pathotype(AAAP),is an important fungal disease of apple.To understand the molecular basis of resistance and pathogenesis in apple leaf spot,the transcriptomes of two apple cultivars‘Hanfu'(HF)(resistant)and‘Golden Delicious'(GD)(susceptible)were analyzed at 0,6,18,24 and 48 h after AAAP inoculation by RNA-Seq.At each time point,a large number of significantly differentially expressed genes(DEGs)were screened between AAAP-inoculated and uninoculated apple leaves.Analysis of the common DEGs at four time points revealed significant differences in the resistance of‘HF'and‘GD'apple to AAAP infection.RLP,RNL,and JA signal-related genes were upregulated in both cultivars to restrict AAAP development.However,genes encoding CNLs,TNLs,WRKYs,and AP2s were only activated in‘HF'as part of the resistance response,of which,some play major roles in the regulation of ET and SA signal transduction.Further analysis showed that many DEGs with opposite expression trends in the two hosts may play important regulatory roles in response to AAAP infection.Transient expression of one such gene MdERF110 in‘GD'apple leaves improved AAAP resistance.Collectively,this study highlights the reasons for differential resistance to AAAP infection between‘HF'and‘GD'apples which can theoretically assist the molecular breeding of disease-resistant apple crops.

MdAIL5 overexpression promotes apple adventitious shoot regeneration by regulating hormone signaling and activating the expression of shoot development-related genes

Adventitious shoot(AS)regeneration is a significant factor in the genetic transformation of horticultural plants.It is also a noteworthy approach to their vegetative propagation.AS regeneration remains highly dependent on the genotype or maturity of explants.We here found that the AS regeneration abilities of apple leaves were positively correlated with MdAIL5 expression.MdAIL5 overexpression dramatically increased AS regeneration efficiency.Notably,MdAIL5 overexpression could restore the AS formation ability of explants to a certain extent,which was lost with an increase in maturity.Endogenous hormone detection revealed that MdAIL5 overexpression changed the contents of auxin,cytokinin(CK),and other hormones in apple leaves.Transcriptome analysis revealed that many genes related to auxin,CK,and brassinolide signaling pathways were significantly and differentially expressed between MdAIL5-overexpressing transgenic apple and wild-type apple plants.Yeast one-hybrid assays,the electrophoretic mobility shift assay,and the dual-luciferase reporter assay revealed that MdAIL5 directly binds to MdARF9 and MdHB14 promoters and positively affects their expression.We here established a model of MdAIL5 regulating AS formation,which acts as a theoretical basis for facilitating genotype-or explant maturity-independent AS regeneration in the future.