Maize and Cercospora zeina transcriptome analysis during gray leaf spot foliar disease

Gray leaf spot (GLS) disease of maize is caused by the fungus Cercospora zeina in African countries, such as South Africa. The plant material was from maize inbred line B73-QTL, which was introgressed with a QTL region for resistance to GLS from the maize inbred line CML444 (Berger et al (2014) BMC Genetics 15 60 www.biomedcentral.com/1471-2156/15/60 ). This QTL was named 10G2_GLS and 10H_GLS from two field trials in KwaZulu-Natal province, South Africa in that study. B73-QTL plants were planted in the field, and subjected to natural infection with C. zeina. This was the same field trial as B73 plants that were sampled for RNAseq and the data reported in Swart et al (2017) Mol Plant Microbe Interact 30 710-724 (2017)(GSE94442). Samples were collected from lower leaves with moderate GLS lesions and younger upper leaves of the same B73-QTL plants with very few immature GLS lesions. The first aim of the experiment was to compare the maize transcriptomes during C.zeina challenge between B73 (from GSE94442 data) and B73-QTL plants (this study). The second aim was to identify novel transcripts expressed from the QTL region, which may underlie the quantitative disease resistance to GLS. The third aim was to identify C. zeina genes expressed in planta during infection. To collect material that reflected a difference between C. zeina infected B73-QTL leaves and control B73-QTL leaf material, samples were collected from two lower GLS infected leaves (second and third leaf internode below ear), and two upper leaves with minimal GLS symptoms (second and third internode above ear), respectively. The two lower leaves from each plant were pooled prior to RNA extraction, and the two upper leaves from each plant were pooled prior to RNA extraction. Upper and lower leaf samples from three maize B73-QTL plants were subjected to RNA sequencing individually. The three maize plants were selected randomly as one plant per row from three rows of ten B73-QTL plants each.