Developmental control of Xa21‐mediated disease resistance in rice

Abstract

Summary The rice resistance gene Xa21 confers resistance against the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo). The molecular genetic mechanism controlling the integration of the Xa21‐mediated disease resistance response with the developmental program in rice is under study in this model system. Reproducible means of infecting plants at certain developmental stages were designed based on the timing of full expansion of the leaf. Xa21‐resistance progressively increases from the susceptible juvenile leaf 2 stage through later stages, with 100% resistance at the adult leaf 9/10 stage. We found that Xa21 expression is independent of plant developmental stage, infection with Xoo, or wounding. Expression of the Xa21 gene transcript is not correlated with expression of Xa21 disease resistance indicating that the developmental regulation of Xa21‐resistance is either controlled post‐transcriptionally or by other factors.

The phenotypic expression of QTLs for partial resistance to barley leaf rust during plant development

“…oryzae in rice cultivars at the tillering stage. Besides tillering, other developmental transitions, such as the juvenile-adult transition and the onset of Xoral development, have been reported to be associated with a constant increase in resistance levels (Hunter et al 1977;Lazarovits et al 1981;Leisner et al 1993;Heath 1994;Abedon and Tracy 1996;Coelho et al1998;Century et al 1999;Hugot et al 1999;Rusterucci et al 2005). The coincident switching oV of Rphq2 and switching on of Rphq4 at tillering suggests that the two QTLs are involved in diVerent defense pathways.…”

“…An increasing number of studies have shown that disease resistance governed by major genes (R genes) or minor genes (quantitative trait loci, QTLs) is, in some cases, plant stage-speciWc (Whalen 2005;Develey-Rivière and Galiana 2007). In recent years, the mode of action of several host growth stage-dependent R genes has been studied in more or less detail (Century et al 1999;Kus et al 2002;Goggin et al 2004). QTL mapping on quantitative resistance has shown that the phenotypic expression of an individual QTL is often plant stage-dependent (e.g., SteVenson et al 1996;Qi et al 1998;Chu et al 2009).…”

The Expression Pattern of a Rice Disease Resistance Gene Xa3/Xa26 Is Differentially Regulated by the Genetic Backgrounds and Developmental Stages That Influence Its Function

“…Full disease resistance usually occurs at adult stages in these systems. Rice Xa21 is expressed at both susceptible and resistant stages, indicating that Xa21-mediated developmentally controlled disease resistance may not be related to its expression (Century et al 1999). Xa3 and Xa21 encoding the same type of proteins share 53% sequence similarity .…”

“…The activity of rice bacterial blight resistance gene Xa21 is developmentally controlled. Xa21-mediated resistance increases progressively from the susceptible juvenile stage to full resistance at the later adult stage (Century et al 1999). Several other rice R genes conferring resistance to Xoo also mediate full disease resistance only in the adult stage (Zhang and Mew 1985;Mew 1987;Goel and Gupta 1990;Ogawa 1993).…”

Molecular determinants of disease and resistance in interactions of Xanthomonas oryzae pv. oryzae and rice

“…oryzae Philippine race 6 (PR6) [5]. The resistance conferred by Xa21 is developmentally regulated, indicating that there are other gene(s) epistatically regulating the defense pathway [15]. The corresponding avr genes for Xa1 and Xa21 have not been isolated from X. oryzae pv.…”