How plant gene expression responds to grazing defoliation is critical for plant re-growth, survival, and composition in the natural and dairy farming grassland environments. Rice, with genome sequence available, was used as a model plant to study grazing-induced pathway selections. When seedlings were 18 cm in height, the top 12 cm was removed by simulated grazing. The gene expression activities within 2 to 24 hours in the remaining aboveground tissues were profiled using the Affymetrix Rice GeneChips and RT-qPCR. The seedlings responded to grazing by immediately adjusting their global gene expression, e.g. enhancing anaerobic respiration, starch-to-sugar conversion, sucrose synthesis, and sugar transport. The results suggest that 1) remaining aboveground tissues used anaerobic respiration as an emergency measure for energy/substrates supply; 2) Sink tissues reduced its demand after 2 h; 3) Sucrose synthesis enhancement around the 24th hour is likely driven by shoot re-growth. In total, the expression activity of 466 genes, involved in signal transduction, miRNA regulation, cell wall modification, metabolism, hormone synthesis, and molecule transporters, had been significantly changed at least twofold. These genes and their biochemical pathways identified provide insights into how plants respond to grazing at the molecular physiology level.
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