Asian Solanaceous & Cucurbits Round Table 27 October 2021 / 2:00 pm - 4:00 pm (GMT+7)

Expert Talk on Crop Improvement - Webinar 6
Wednesday the 27th of October 2021
2:00pm - 4:00 pm ICT (GMT+7)

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Theme: “Perspectives on Disease Resistance Breeding Using S-Genes”

SPEAKER PROFILE & ABSTRACT

Dr. Sota Koeda
Associate Professor, Faculty of Agriculture
Kindai University, Japan

Profile
Dr. Sota Koeda received his Ph.D. in horticulture science from Kyoto University (2011) in Japan. He then started his career at Kyoto University as an Assistant Professor. In 2015, he joined the Faculty Agriculture of the Kindai University in Japan and is currently an Associate Professor at the Laboratory of Horticultural Science. The main focus of his research group is the breeding of begomovirus resistance in Solanaceae (pepper, tomato, eggplant) and Cucurbit (cucumber and melon) crops. His research group has recently identified the begomovirus resistance gene for the first time in pepper.

Abstract
Identification of Begomovirus Resistance Gene in Capsicum and the Future Perspective for Resistance Breeding
Pepper yellow leaf curl disease caused by begomoviruses seriously affects pepper (Capsicum spp.) production in a number of regions around the world. Ty genes of tomato, which confer resistance to the tomato yellow leaf curl virus, are the only begomovirus resistance genes cloned to date. We have been conducting identification of pepper-infecting begomoviruses in the field and constructing a highly efficient inoculation method of begomoviruses for resistance evaluation in pepper. In this presentation, I want to focus on the newly identified begomovirus resistance genes in Capsicum annuum by our research group. BaPep-5 was identified as a novel source of resistance against pepper yellow leaf curl Indonesia virus (PepYLCIV) and pepper yellow leaf curl Aceh virus (PepYLCAV). A single recessive locus, which we named pepper yellow leaf curl disease virus resistance 1 (pepy-1), responsible for PepYLCAV resistance in BaPep-5 was identified on chromosome 5 in an F2 population derived from a cross between BaPep-5 and the begomovirus susceptible accession BaPep-4. In the target region spanning 34 kb, a single candidate gene, the messenger RNA surveillance factor Pelota, was identified. Whole-genome resequencing of BaPep-4 and BaPep-5 and comparison of their genomic DNA sequences revealed a single nucleotide polymorphism (A to G) located at the splice site of the 9th intron of CaPelota in BaPep-5, which caused the insertion of the 9th intron into the transcript, resulting in the addition of 28 amino acids to CaPelota protein without causing a frameshift. Virus-induced gene silencing of CaPelota in the begomovirus susceptible pepper No.218 resulted in the gain of resistance against PepYLCIV, a phenotype consistent with BaPep-5. The DNA marker developed in this study will greatly facilitate marker-assisted breeding of begomovirus resistance in peppers.

Dr. Yuling Bai
Professor – Plant Breeding
Wageningen University, Netherlands

Profile
Dr. Yuling Bai is a Professor at Plant Breeding, Wageningen University & Research (WUR), where she leads the research group - “Breeding for Resistance”. Her research focuses on the understanding of genetic and molecular mechanisms underlying disease resistances to different pathogens in mainly vegetables and potato. Various genetic and genomics approaches are exploited to discover novel natural resistance genes and to study their interactions with the corresponding pathogen. In 2009, she promoted the susceptibility (S) gene concept in disease resistance breeding. She studied Msc Biotechnology at WUR and graduated cum laude, and earned her PhD at Plant Breeding of WUR. She is the Chairperson of Section Vegetables in EUCARPIA (European Association for Research on Plant Breeding) and member of WUR Academic Board. She has authored over 100 papers in peer reviewed journals.

Abstract
Susceptibility Reversed: Edited Plant S-Genes for Disease Resistance
Plants have evolved complex defence mechanisms to avoid invasion of potential pathogens. Despite this, adapted pathogens deploy effector proteins to manipulate plant susceptibility (S) genes, rendering plant defences ineffective. Plant genes that facilitate a compatible interaction with the pathogen can be considered an S gene. Although S genes are exploited by pathogens to promote disease, their mutation can lead to durable, recessively inherited and non-host-like resistance in plants. Till now, application of mutant S genes in breeding of resistant crops is limited, due to potential pleiotropy. With more and more S genes identified, our knowledge into plant susceptibility and how S genes can be edited with advanced techniques will be further expanded. Such knowledge will open up new possibilities for the modification of S genes. In this talk, I will introduce the S-gene concept and highlight the potential of using mutated S genes in breeding crops with resistance to pathogens.

Dr. Henk Schouten
Senior Scientist – Plant Breeding
Wageningen University, Netherlands

Profile
Dr Henk J. Schouten (60) is senior scientist at Plant Breeding, Wageningen UR. He performs research on plant breeding, especially disease resistance. He developed together with colleagues the concept of cisgenesis, which is genetic modification of plants, using natural genes from crossable relatives only. He works on genetic mapping and functional characterisation of resistance genes and susceptibility genes in cucurbits and tomato. Since a few years he is also actively involved in genome editing and targeted recombination, using CRISPR-Cas. He studied plant sciences at the Wageningen University and graduated cum laude, and earned his PhD at the department of Phytopathology of Wageningen UR. He was chairman of the Agricultural group in the Commission of Genetic Modification from 2004 till 2012 and member of the executive board of this commission. He has authored over 130 papers in peer reviewed journals.

Abstract
MLO and Amino Acid Permease (AAP) Susceptibility Genes in Cucumber
Cucumber has 13 MLO-¬genes. Three out of these genes belong to MLO-clade V, suggestion these are possibly susceptibility genes (S-genes) for powdery mildew (PM). We detected a natural knock-out of one of these three Clade V genes, CsaMLO8, caused by a large insertion of a transposable element. This mutation led to partial resistance to PM, especially of the hypocotyl of cucumber. We showed by means of complementation in an mlo-mutant if tomato, that CsaMLO8 but also the two other Clade V MLO-genes CsaMLO1 and CsaMLO11, are S-genes for PM. However, we did not find natural knock-out alleles for the latter two genes yet.

Cucurbit Downy Mildew (DM), caused by the obligate biotroph Pseudoperonospora cubensis, is a destructive disease in cucumber. A valuable source of DM resistance is the Indian cucumber accession PI 197088 that harbors several QTLs contributing to quantitatively inherited DM resistance. With a combination of fine-mapping and transcriptomics, we identified Amino Acid Permease 2A (CsAAP2A) as a candidate gene for QTL DM4.1.3. Whole-genome and Sanger sequencing revealed the insertion of a Cucumis Mu-like element (CUMULE) transposon in the allele of the resistant line NIL DM4.1.3. To confirm whether loss of CsAAP2A contributes to partial DM resistance, we performed TILLING on a DM susceptible cucumber genotype in order to identify an additional csaap2a mutant, which indeed was partially DM resistant.

In view of the loss of the putative function as amino acid transporter, we measured amino acids in leaves. We found that DM-inoculated leaves of NIL DM4.1.3 (with the csaap2a mutation) contained significantly less amino acids than WT cucumber. The decreased flow of amino acids towards infected leaves in csaap2a plants compared to wild type might explain the resistant phenotype of the mutant, as this will limit the available nutrients for the pathogen and thereby its fitness.

To examine whether AAP genes play a conserved role as susceptibility factors in plant-oomycete interactions, we made targeted mutations in two AAP genes from tomato and studied the effect on susceptibility to Phytophthora infestans. We conclude that not only CsAAP2A but also SlAAP5A/SlAAP5B are susceptibility genes for oomycete pathogens.

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