Loss-of-Function Mutations in CsMLO1 Confer Durable Powdery Mildew Resistance in Cucumber (Cucumis sativus L.)

Abstract

Powdery mildew (PM) is a serious fungal disease of cucumber worldwide. The identification of resistance genes is very important for resistance breeding to ensure cucumber production. Here, natural loss-of-function mutations at an MLO homologous locus, CsMLO1, were found to confer durable PM resistance in cucumber. CsMLO1 encoded a cell membrane protein, was mainly expressed in leaves and cotyledons, and was up-regulated by PM at the early stage of host–pathogen interaction. Ectopic expression of CsMLO1 rescued the phenotype of the PM resistant Atmlo2 Atmlo12 double mutant to PM susceptible in Arabidopsis. Domesticated and wild resistant cucumbers originating from various geographical regions of the world were found to harbor three independent natural mutations that resulted in CsMLO1 loss of function. In addition, between the near-isogenic lines (NILs) of PM resistant and susceptible, S1003 and NIL(Pm5.1), quantitative RT-PCR revealed that there is no difference at expression levels of several genes in the pathways of ethylene, jasmonic acid or salicylic acid. Moreover, the two NILs were used for transcriptome profiling to explore the mechanism underlying the resistance. Several genes correlated with plant cell wall thickening are possibly involved in the PM resistance. This study revealed that loss of function of CsMLO1 conferred durable PM resistance, and that this loss of function is necessary but alone may not be sufficient for PM resistance in cucumber. These findings will facilitate the molecular breeding of PM resistant varieties to control this destructive disease in cucumber.

Identification of novel loci and candidate genes for resistance to cucumber powdery mildew using GWAS

“…The frequency distributions of DI indicated that PM resistance of cucumber were controlled by multiple loci (Fig. 2), which is consistent with previous studies [7,14].…”

“…Most of the QTLs showed recessive inheritance, indicating that the resistance is governed by loss-offunction mutant alleles of certain susceptible genes [12,13]. Indeed, a mutant allele of the cucumber susceptibility gene CsaMLO8 (named as CsMLO1 in [14] explains the contribution to PM resistance by the QTL pm5.1 [15]. Except for the pm5.1, causal genes of other mapped QTLs for PM resistance in cucumber have not been discovered yet.…”

STAYGREEN, STAY HEALTHY: a loss‐of‐susceptibility mutation in the STAYGREEN gene provides durable, broad‐spectrum disease resistances for over 50 years of US cucumber production

“…A prime example of the lossof-susceptibility mechanism is the barley mlo (mildew locus o) gene that encodes a defective, integral membrane protein which is important for infection of the powdery mildew pathogen (B€ uschges et al, 1997;Humphry et al, 2006Humphry et al, , 2010. The mlomediated powdery mildew resistance has been found in wheat, grapevine, rice, tomato and cucumber (Elliott et al, 2002;Bai et al, 2008;Nie et al, 2015;Pessina et al, 2016;Acevedo-Garcia et al, 2017). The wheat Lr34, Lr67 and Yr36 also belong to the loss-of-susceptibility R genes.…”

Mitochondrial genome of thePodosphaera xanthii: a plant pathogen causes powdery mildew in cucurbits

“…Podosphaera xanthii is the plant pathogen belonging to Erysiphaceae family, and the fungal belonging to this family cause the powdery mildew disease in most cultivated plants/ crops, particularly, P. xanthii is the pathogen for cucurbits (Mart ınez-Cruz et al 2018). In Korea, this fungus effects various crops in cucurbits, such as melon (Hong et al 2018), cucumber (Nie et al 2015), and other weed-like plants, such as Cirsium japonicum (Lee 2012). This powdery mildew pathogens have specific molecular mechanism called haustoria, which is used to invade the host cells (Lee 2012;Hong et al 2018).…”

“…This powdery mildew pathogens have specific molecular mechanism called haustoria, which is used to invade the host cells (Lee 2012;Hong et al 2018). This fungus mostly cause serious economic loss in greenhouse environment, which decide the yield of the most cucurbits (Nie et al 2015).…”