Overexpression of CRK8 Gene in Sugar Beet line Resistant to Beet Curly Top disease

Resistance to Beet curly top virus (BCTV) is an essential trait for all cultivars grown in western USA.  Currently insecticides are used to compliment low and moderate levels of resistance in commercial varieties. To identify genes regulating resistance to BCT, differential gene expression was studied via RNA-sequencing using an exceptionally resistant doubled haploid line (KDH13-PI663862) compared to a susceptible breeding line (K19-19). KDH13 was subjected to 7 treatments: infested with non-infectious leafhoppers, infected with leafhoppers population carrying a single, two, or three strains, and control healthy leaf. The susceptible line was infected with the three strains.  Leaf samples were sequenced in a HiSeq2500 and data was analyzed using TopHat and Cufflinks software. All sequences were aligned to the RefBeet-1.2. Based on 28 pair-wise comparisons, differentially expressed genes were determined with a cuttoff of false-discovery-rate; FDR<0.05 and a LogFC (expression fold change) >2.0 or <-2.0. In this study we are focusing on the intricate patterns of the expression levels of the protein-coding gene CRK8 (cysteine-rich receptor-like protein kinase), induced by beet leafhopper infestation and BCTV. There are 171 members of the CRK8 (AT4G23160) that were differentially expressed in comparisons between healthy, infested, and infected leaf of KDH13 and K19-19. In KDH13 a single member of the CRK8 showed a consistent overexpression after leafhopper infestation or infection with the three strains at LogFC of 2.3 and FDR <1.0^-4. qPCR analysis was conducted to support these results for 4 CRK8 members using tissue from the same plants used for the initial RNA sequencing. The qPCR results confirm overexpression of two of the CRK8 members in the resistant line.