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Poster: Molecular & Cellular Plant-Microbe Interactions: MPMI


Macrophomina phaseolina induces stalk senescence in charcoal rot susceptible sorghum genotypes through up-regulated host chlorophyllase-2 biosynthesis
A. BANDARA (1), D. Weerasooriya (1), S. Liu (1), C. Little (1) (1) Kansas State University, U.S.A.

Charcoal rot (Macrophomina phaseolina, MP) and Fusarium stalk rot (Fusarium thapsinum, FT) are important sorghum diseases worldwide. An RNA-Seq experiment was conducted to explore the interaction of MP and FT with known resistant and susceptible sorghum genotypes. SC599 (R) and TX7000 (S) sorghum lines were grown in the greenhouse and inoculated with FT, MP, and phosphate-buffered saline (control). RNA extracted from stem tissues at 2, 7, and 30 days post-inoculation (d.p.i.) was subjected to RNA-Seq. At 7 d.p.i., a gene that encodes chlorophyllase-2 (Sb02g012300) showed two and 200-fold up-regulation in FT- and MP-inoculated Tx7000, respectively. SC599 did not show a significant differential expression. To confirm the effect of up-regulated chlorophyllase-2, stalk chlorophyll was extracted with acetone from two pathogen- and mock-inoculated resistant (SC599, SC35) and susceptible (Tx7000, BTx3042) sorghum lines at 7 d.p.i. Total chlorophyll content (mg/g stalk) was computed using spectrophotometer readings. Compared to control, MP significantly reduced total chlorophyll of Tx7000 (control, 1.56; MP, 0.40) and BTx3042 (control, 1.45; MP, 0.63) (P < 0.016). No such effect was evident with the two resistant genotypes. FT did not significantly affect the chlorophyll content of any genotype. Results revealed the ability of MP to induce stalk senescence through increased chlorophyll degradation, which contributes to the enhanced vulnerability to this necrotrophic fungus.