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Summary: Glomerella leaf spot (GLS), caused by the fungus Colletotrichum fructicola, is considered one of the most destructive diseases affecting apples. The VQ‐WRKY complex plays a crucial role in the response of plants to biotic stresses. However, our understanding of the defensive role of the VQ‐WRKY complex on woody plants, particularly apples, under biotic stress, remains limited. In this study, we elucidated the molecular mechanisms underlying the defensive role of the apple MdVQ37‐MdWRKY100 module in response to GLS infection. The overexpression of MdWRKY100 enhanced resistance to C. fructicola, whereas MdWRKY100 RNA interference in apple plants reduced resistance to C. fructicola by affecting salicylic acid (SA) content and the expression level of the CC‐NBS‐LRR resistance gene MdRPM1. DAP‐seq, Y1H, EMSA, and RT‐qPCR assays indicated that MdWRKY100 inhibited the expression of MdWRKY17, a positive regulatory factor gene of SA degradation, upregulated the expression of MdPAL1, a key enzyme gene of SA biosynthesis, and promoted MdRPM1 expression by directly binding to their promotors. Transient overexpression and silencing experiments showed that MdPAL1 and MdRPM1 positively regulated GLS resistance in apples. Furthermore, the overexpression of MdVQ37 increased the susceptibility to C. fructicola by reducing the SA content and expression level of MdRPM1. Additionally, MdVQ37 interacted with MdWRKY100, which repressed the transcriptional activity of MdWRKY100. In summary, these results revealed the molecular mechanism through which the apple MdVQ37‐MdWRKY100 module responds to GLS infection by regulating SA content and MdRPM1 expression, providing novel insights into the involvement of the VQ‐WRKY complex in plant pathogen defence responses. [ABSTRACT FROM AUTHOR]

Drought stress is an environmental factor that seriously threatens plant growth, development and yield. VQ proteins are transcriptional regulators that have been reported to be involved in plant growth, development and the responses to biotic and abiotic stressors. However, the relationship between VQ proteins and drought stress has not been well documented in plants. In this study, overexpressing the apple VQ motif-containing protein (MdVQ37) gene in apple plants markedly reduced the tolerance to drought. Physiological and biochemical studies further demonstrated lower enzymatic activities and decreased photosynthetic capacity in transgenic lines compared with wild-type (WT) plants under drought stress. Ultrastructural analysis of leaves showed that the leaves and palisade tissues from the transgenic lines were significantly thinner than those from WT plants. Salicylic acid (SA) analysis indicated that overexpression of MdVQ37 increased the accumulation of 2,5-DHBA by up-regulating the expression of the SA catabolic gene, which ultimately resulted to a significant reduction in endogenous SA content and the disruption of the SA-dependent signaling pathway under drought stress. Applying SA partially increased the survival rate of the transgenic lines under drought stress. These results demonstrate that the regulatory function of apple MdVQ37 is implicated in drought stress, through a change in leaf development and SA homeostasis. This study provides novel insight into understanding the multiple functions of VQ proteins. [ABSTRACT FROM AUTHOR]

Drought seriously threatens the growth, development, and yield of crops. WRKY transcription factors (TFs) play important roles in abiotic stress responses. However, the study of WRKY TFs in woody plant apple (Malus domestica) in terms of drought tolerance regulation is limited. This study aimed to functionally characterize an apple group IIc WRKY gene MdWRKY56. The transcription abundance of MdWRKY56 was significantly upregulated under drought stress. The subcellular localization analysis revealed that the MdWRKY56 protein localized to the nucleus. Transcriptional activation experiments proved that MdWRKY56 had transcriptional activity in yeast, and its N-terminal played a decisive role in this activity. The functional analysis using MdWRKY56 transgenic Arabidopsis , apple calli, and apple plants indicated that the MdWRKY56 TF functioned positively in the modulation of osmotic and drought stress tolerance, with the MdWRKY56-overexpressed transgenic materials showing lower electrolyte leakage, malondialdehyde (MDA) content, and reactive oxygen species (ROS) accumulation, and higher fresh weight, proline content, and antioxidant enzyme activities. In conclusion, our findings indicated that MdWRKY56 served as an important positive regulator of drought stress tolerance in apple. • The transcription abundance of MdWRKY56 was significantly upregulated under drought stress. • Transcriptional activation activity and nuclear localization of MdWRKY56 were confirmed. • Overexpression of MdWRKY56 enhanced tolerance to osmotic and drought stresses in transgenic materials. [ABSTRACT FROM AUTHOR]