Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes Fusarium wilt of banana, the most devastating disease on a banana plant. The genome of Foc TR4 encodes many candidate effector proteins. However, little is known about the functions of these effector proteins on their contributions to disease development and Foc TR4 virulence. Here, we discovered a secreted metalloprotease, FocM35_1, which is an essential virulence effector of Foc TR4. FocM35_1 was highly upregulated during the early stages of Foc TR4 infection progress in bananas. The FocM35_1 knockout mutant compromised the virulence of Foc TR4. FocM35_1 could interact with the banana chitinase MaChiA, and it decreased banana chitinase activity. FocM35_1 induced cell death in Nicotiana benthamiana while suppressing the INF1-induced hypersensitive response (HR), and its predicted enzymatic site was required for lesion formation and the suppression to INF1-induced HR on N. benthamiana leaves. Importantly, treatment of banana leaves with recombinant FocM35_1 accelerates Foc TR4 infection. Collectively, our study provides evidence that metalloprotease effector FocM35 seems to contribute to pathogen virulence by inhibiting the host immunity.

Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is well-known as the causal agent of Fusarium wilt of banana and is one of the most destructive phytopathogens for banana plants. The molecular mechanisms underlying Foc TR4 virulence remain elusive. Here, we demonstrate that a cerato-platanin (CP) protein, FocCP1, functions as a virulence factor that is required by Foc TR4 for penetration and full virulence. The FocCP1 gene was expressed in every condition studied, showing a high transcript level in planta at the early stage of infection. Infiltration of the recombinant FocCP1 protein induced significant cell death and upregulated defence-related gene expression. FocCP1 knock-out strains showed a significant decrease in aerial growth rather than aqueous growth, which is reminiscent of hydrophobins. Furthermore, deletion of FocCP1 significantly reduced virulence and dramatically reduced infective growth in banana roots, likely resulting from a defective penetration ability. Taken together, the results of this study provide novel insight into the function of the recently identified FocCP1 as a virulence factor in Foc TR4.

Banana is one of the most important fruits in the world due to its status as a major food source for more than 400 million people. Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes substantial losses of banana crops every year, and molecular host resistance mechanisms are currently unknown. We here performed a genomewide analysis of the autophagy-related protein 8 (ATG8) family in a wild banana species. The banana genome was found to contain 10 MaATG8 genes. Four MaATG8s formed a gene cluster in the distal part of chromosome 4. Phylogenetic analysis of ATG8 families in banana, Arabidopsis thaliana, citrus, rice, and ginger revealed five major phylogenetic clades shared by all of these plant species, demonstrating evolutionary conservation of the MaATG8 families. The transcriptomic analysis of plants infected with Foc TR4 showed that nine of the MaATG8 genes were more highly induced in resistant cultivars than in susceptible cultivars. Finally, MaATG8F was found to interact with MaATG4B in vitro (with yeast two-hybrid assays), and MaATG8F and MaATG4B all positively regulated banana resistance to Foc TR4. Our study provides novel insights into the structure, distribution, evolution, and expression of the MaATG8 family in bananas. Furthermore, the discovery of interactions between MaATG8F and MaATG4B could facilitate future research of disease resistance genes for the genetic improvement of bananas.

There is a renewed interest, especially among organic growers, in using either white sweetclover (Melilotus alba Desr.) or yellow sweetclover [M. officinalis (L.) Lam.] as cover crops. Sweetclover cultivars and tillage practices have changed since these crops were widely used as cover crops in the first half of the 20th century. Experiments were initiated in 1999, 2000, and 2002 to compare the effect of high- and low-coumarin cultivars and crop termination methods on weed suppression, available soil N, moisture conservation and following crop yield. Weed suppression was usually more effective when sweetclover residues were left on the surface than when removed as hay. Sweetclover termination at 70% bloom was often more effective in suppressing weeds than termination at the bud stage. In the summer and fall after termination, surface residues of Yukon, a high-coumarin and drought-tolerant cultivar, reduced lamb’s-quarters (Chenopodium album L.) density by > 80% compared with the no sweetclover check and essentially eliminated flixweed [Descurainia Sophia (L). Webb]. In the following spring, Yukon reduced kochia [Kochia scoparia (L.) Schrad.] density by > 80% and wild oat (Avena fatua L.) biomass by > 30% compared with the no sweetclover check. There was no difference in available N for a following crop between treatments with surface residue and cultivated fallow. Available soil moisture was about 10 mm less after the highest yielding sweetclover cultivars than after cultivated fallow, but subsequent wheat yield was not reduced. Maximum wheat yields were obtained after Yukon and Arctic sweetclover were grown as cover crops. It may be possible for organic growers to manage weeds with sweetclover in a reduced tillage system that leaves most of the plant residues on the soil surface. Key words: Cover crop, weed suppression, allelopathy, nitrogen, soil moisture

Citrus Huanglongbing (HLB) is the most destructive citrus disease worldwide. The etiological agent responsible for this disease is “Candidatus Liberibacter asiaticus” (CLas), a phloem-restricted bacterium transmitted by psyllid vectors. To date, effective practical strategies for curing Citrus HLB remain elusive. Additionally, no susceptibility genes associated with HLB have been identified in Citrus species, thereby complicating the application of gene-editing techniques such as CRISPR-Cas9 to enhance resistance to HLB. The co-chaperone DnaJ plays a crucial role in protein folding and the regulation of various physiological activities, and it is also associated with multiple pathological processes. DnaJ has been extensively studied in many species, including Arabidopsis, rice, and wheat. However, there is limited information available regarding the DnaJ gene family in citrus. In this study, we conducted a comprehensive genome-wide analysis of the DnaJ family genes in various Citrus species. The Citrus genome was identified to contain 86 DnaJ genes, which were unevenly distributed across nine chromosomes. Phylogenetic analysis indicated that these genes could be classified into six distinct groups. Furthermore, transcriptomic analysis revealed that nine DnaJ genes exhibited significantly higher induction in HLB-infected samples relative to non-HLB-infected Citrus. Cis-acting elements within the promoters of DnaJ genes were also examined, revealing the presence of hormone and defense/stress responsiveness elements (TC-rich) distributed on the ClDJC24 gene. The results were validated using quantitative real-time PCR (qRT-PCR). Additionally, the silencing of ClDJC24 suggested that this gene negatively regulates disease resistance in Citrus. Our study provided useful clues for further functional characterization and constructed a theoretical foundation for disease-resistant breeding in Citrus.

Banana is one of the most important fruits in the world due to its status as a major food source for more than 400 million people. Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes substantial losses of banana crops every year, and molecular host resistance mechanisms are currently unknown. We here performed a genome-wide analysis of the autophagy related protein 8 (ATG8) family in a wild banana species. The banana genome was found to contain 10 MaATG8 genes. Four MaATG8s formed a gene cluster in the distal part of chromosome 4. Phylogenetic analysis of ATG8 families in banana, Arabidopsis thaliana, Citrus, rice, and ginger revealed five major phylogenetic clades shared by all of these plant species, demonstrating evolutionary conservation of the MaATG8 families. The transcriptomic analysis of plants infected with Foc TR4 showed that almost all of the MaATG8 genes were more highly induced in resistant cultivars than in susceptible cultivars. Finally, MaATG8F was found to interact with MaATG4B in vitro (with yeast two-hybrid assays), and MaATG8F and MaATG4B all positively regulated banana resistance to Foc TR4. Our study provides novel insights into the structure, distribution, evolution, and expression of the MaATG8 family in bananas. Furthermore, the discovery of interactions between MaATG8F and MaATG4 could facilitate future researches of disease resistance genes for genetic improvement of bananas.