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

Gray leaf spot (GLS) disease of maize can be caused by either of two sibling fungal species Cercospora zeina or Cercospora zeae-maydis. These species differ in geographical distribution, for example to date only C. zeina is associated with GLS in African countries, such as South Africa. Maize inbred line B73, which is susceptible to GLS, was planted in the field, and subjected to natural infection with C. zeina. Samples were collected from lower leaves with substantial GLS lesions and younger upper leaves of the same plants with very few immature GLS lesions. The first aim of the experiment was to determine which maize genes are induced in response to C. zeina infection. The second aim was to identify C. zeina genes expressed in planta during a compatible interaction. The third aim was to determine whether the C. zeina cercosporin biosynthetic (CTB) genes are expressed in planta. C. zeina fails to produce cercosporin in vitro in contrast to C. zeae-maydis. Cercosporin is a phytotoxin that is thought to play a role in pathogenicity of several Cercospora spp., however its role in the pathogenicity strategy of C. zeina is currently under investigation. Overall design: To collect material that reflected a difference between C. zeina infected B73 leaves and control B73 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 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 plants each.

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Swart V, Crampton BG, Ridenour JB, Bluhm BH, Olivier NA, Meyer JJM, Berger DK