Abstract Transcriptional profiling has identified genes
associated with adaptive responses to phosphorus (P)
deficiency; however, distinguishing stress response from
tolerance has been difficult. We report gene expression
patterns in two rice genotypes (Nipponbare and NIL6-4
which carries a major QTL for P deficiency tolerance
(Pup1)) grown in soil with/without P fertilizer. We tested
the hypotheses that tolerance of NIL6-4 is associated with
(1) internal P remobilization/redistribution; (2) enhanced P
solubilization and/or acquisition; and (3) root growth
modifications that maximize P interception. Genes responding
to P supply far exceeded those differing between genotypes. Genes associated with internal P remobilization/
redistribution and soil P solubilization/uptake were stress
responsive but often more so in intolerant Nipponbare.
However, genes putatively associated with root cell wall
loosening and root hair extension (xyloglucan endotransglycosylases/hydrolases
and NAD(P)H-dependent oxidoreductase)
showed higher expression in roots of tolerant
NIL6-4. This was supported by phenotypic data showing
higher root biomass and hair length in NIL6-4.