High activities and mRNA expression of pyrophosphate-fructose-6-phosphate-phosphotransferase and 6-phosphofructokinase are induced as a response to Rhizoctonia solani infection in rice leaf sheaths

Rice sheath blight disease caused by Rhizoctonia solani Kuhn results in significant yield and quality losses in rice growing areas worldwide. The glycolytic pathway is important in the resistance response to R. solani infection in rice. This study examined one of the regulatory steps in this pathway catalyzed by pyrophosphate-fructose-6-phosphate-phosphotransferase (PFP) and 6-phosphofructokinase (PFK). PFP and PFK activity in R. solani-infected rice plants increased. The mRNA expression of PFP/PFK isozymes showed that PFK 1, 2, 4 and 5 in the resistant line at 1 dpi were high as compared to the gradual increase observed in the expression of all PFP isozymes. Also PFK 1, PFK 3, PFK 4, PFK 5, PFP 2 and PFP 5 were adaptive to sheath blight disease infection and linked to defence response while, the expressions of PFK 2, PFP 1, PFP 3 and PFP 4 although adaptive, were not specific to R. solani infection. These observations provide evidence that (a) both PFP and PFK have isozymes that play an adaptive role after R. solani infection but while those of PFK are expressed at higher levels within a short time after infection those of PFP are expressed gradually, (b) the adaptive activation of PFP in R. solani-infected rice plants is correlated with the paired expression of its α- and β-subunits as shown by PFP 2 and PFP 5, and (c) the expression of some α-subunits is not specific to R. solani infection as shown by PFP 1, PFP 3 and PFP 4.