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Glomerella leaf spot (GLS), caused by the fungal pathogen Colletotrichum fructicola, significantly threatens apple production. Some resistances to plant disease are mediated by the accumulation of nucleotide‐binding site and leucine‐rich repeat (NBS‐LRR) proteins that are encoded by a major class of plant disease resistance genes (R genes). However, the R genes that confer resistance to GLS in apple remain largely unclear. Malus hupehensis YT521‐B homology domain‐containing protein 2 (MhYTP2) was identified as an N6‐methyladenosine RNA methylation (m6A) modified RNA reader in our previous study. However, whether MhYTP2 binds to mRNAs without m6A RNA modifications remains unknown. In this study, we discovered that MhYTP2 exerts both m6A‐dependent and ‐independent functions by analysing previously obtained RNA immunoprecipitation sequencing results. The overexpression of MhYTP2 significantly reduced the resistance of apple to GLS and down‐regulated the transcript levels of some R genes whose transcripts do not contain m6A modifications. Further analysis indicated that MhYTP2 binds to and reduces the stability of MdRGA2L mRNA. MdRGA2L positively regulates resistance to GLS by activating salicylic acid signalling. Our findings revealed that MhYTP2 plays an essential role in the regulation of resistance to GLS and identified a promising R gene, MdRGA2L, for use in developing apple cultivars with GLS resistance. [ABSTRACT FROM AUTHOR]

SUMMARY: Malic acid is a major organic acid component of apples and a crucial determinant of fruit organoleptic quality. A candidate gene for malic acid content, designated MdMa1, was previously identified in the Ma locus, which is a major quantitative trait locus (QTL) for apple fruit acidity located on the linkage group 16. Region‐based association mapping to detect candidate genes in the Ma locus identified MdMa1 and an additional MdMYB21 gene putatively associated with malic acid. MdMYB21 was significantly associated with fruit malic acid content, accounting for ~7.48% of the observed phenotypic variation in the apple germplasm collection. Analyses of transgenic apple calli, fruits and tomatoes demonstrated that MdMYB21 negatively regulated malic acid accumulation. The apple fruit acidity‐related MdMa1 and its tomato ortholog, SlALMT9, exhibited lower expression profiles in apple calli, mature fruits and tomatoes in which MdMYB21 was overexpressed, compared with their corresponding wild‐type variety. MdMYB21 directly binds to the MdMa1 promoter and represses its expression. Interestingly, a 2‐bp variation in the MdMYB21 promoter region altered its expression and regulation of its target gene, MdMa1, expression. Our findings not only demonstrate the efficiency of integrating QTL and association mapping in the identification of candidate genes controlling complex traits in apples, but also provide insights into the complex regulatory mechanism of fruit malic acid accumulation. Significance Statement: Fruit acidity is a complex quantitative trait that is regulated by one or more major and/or numerous minor genes. Region‐based association mapping was performed, and identified two candidate genes, MdMa1 and MdMYB21, which were associated with malic acid content in the Ma locus at linkage group (LG)16. Furthermore, MdMYB21 could negatively regulate malic acid accumulation in apple fruits by repressing the MdMa1 expression. [ABSTRACT FROM AUTHOR]

Hail, known as an agricultural meteorological disaster, can substantially constrain the growth of the apple industry. Presently, apple orchards use a variety of colored (photo-selective) hail nets as a preventative measure. However, it is unclear which color proves most effective for apple orchards. This study provides a systematic investigation of the impact of four photo-selective colored hail nets (white, blue, black, and green; with white being the control) on the microenvironment of apple orchards, fruit tree development, fruit quality, and yield over a two-year period (2020–2021). Different photo-selective nets do not evidently alter the intensity of light, although the nets' shading effects decrease in the order from black to green to blue. Among them, blue nets increased the proportion of blue light, while green nets enhanced the proportion of green light. On the other hand, black, green, and blue nets diminished the proportion of red and far-red light. Such photo-selective nets effectively lowered soil temperature but did not have an impact on relative humidity and air temperature. Encasing apple trees with blue nets promoted growth, increasing shoot length, thickness, leaf area, and water content, while simultaneously decreasing leaf thickness. Black nets had comparable effects, although the impacts of green nets were inconsistent. Different photo-selective nets did not significantly influence the leaf shape index or overall chlorophyll content. However, black and green nets reduced the chlorophyll a/b ratio, while blue nets slightly boosted this ratio. Additionally, blue nets proved beneficial for apple trees' photosynthesis. With the employment of a principal component analysis and comprehensive evaluation, this study concludes that blue nets offer the most favorable environmental conditions for apple growth while protecting apple orchards against hail, compared to black, white, and green nets. [ABSTRACT FROM AUTHOR]

Macroautophagy/autophagy is a conserved degradation pathway in eukaryotes that is required for recycling unwanted intracellular components, maintaining homeostasis, and coping with biotic and abiotic stresses. Pathogens have evolved to subvert autophagic machinery by secreting host cell-entering effector proteins. Here, we provided evidence that an apple autophagy-related gene MdATG8i, activated autophagy and contributed to resistance against Valsa canker caused by Valsa Mali (Vm) when being overexpressed in apple. MdATG8i interacted with a plastid elongation factor Tu (MdEF-Tu) which became insoluble and aggregated during Vm infection and was degraded through the autophagy pathway. Intriguingly, we identified a highly-induced effector secreted from Vm, Vm1G-1794, which competitively interacted with MdATG8i, suppressed autophagy, and depleted MdEF-Tu out of MdATG8i complexes. The formation of stable MdEF-Tu aggregates caused by Vm1G-1794 promoted the susceptibility of apple to Vm. Overall, our study demonstrated that MdATG8i contributed to Vm resistance by targeting and degrading MdEF-Tu, and Vm1G-1794 competed with MdEF-Tu to target MdATG8i and prevent MdEF-Tu degradation, thus favoring infection. Abbreviations: 35S: cauliflower mosaic virus 35S promoter; AIM: ATG8-interacting motif; ATG8–PE: ATG8 conjugated with phosphatidylethanolamine; BiFC: biomolecular fluorescence complementation; Con A: concanamycin A; Co-IP: co-immunoprecipitation; DEPs: differentially expressed proteins; DMSO: dimethyl sulfoxide; GFP: green fluorescent protein; hpt: hours post-treatment; LCI: luciferase complementation imaging; MdATG8i: autophagy-related protein 8i in Malus domestica; MDC: monodansylcadaverine; MdEF-Tu: elongation factor Tu in Malus domestica; MdNBR1: neighbor of BRCA1 in Malus domestica; N. benthamiana: Nicotiana benthamiana; OE: overexpression; PAMP: pathogen-associated molecular pattern; PTI: pattern-triggered immunity; qRT-PCR: quantitative reverse transcription PCR; RFP: red fluorescent protein; RNAi: RNA interference; ROS: reactive oxygen species; Ub: ubiquitin; V. Mali: Valsa Mali; WT: wild-type plant; YFP: yellow fluorescent protein [ABSTRACT FROM AUTHOR]