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

Abstract

Genetic background and developmental stage influence the function of some disease resistance (R) genes. The molecular mechanisms of these modifications remain elusive. Our results show that the two factors are associated with the expression of the R gene in rice Xa3 (also known as Xa26)-mediated resistance to Xanthomonas oryzae pv. oryzae (Xoo), which in turn influences the expression of defenseresponsive genes. The background of japonica rice, one of the two major subspecies of Asian cultivated rice, facilitates the function of Xa3 more than the background of indica rice, another rice subspecies. Xa3 expression gradually increases from early seedling stage to adult stage. Japonica plants carrying Xa3 regulated by the native promoter showed an enlarged resistance spectrum (i.e., resistance to more Xoo races), an increased resistance level (i.e., further reduced lesion length), and whole-growth-stage resistance compared to the indica rice; this enhanced resistance was associated with an increased expression of Xa3 throughout the growth stages in the japonica plants, which resulted in enhanced expression of defenseresponsive genes. Overexpressing Xa3 with a constitutive strong promoter further enhanced rice resistance due to further increased Xa3 transcripts in both indica and japonica backgrounds, whereas regulating Xa3 with a pathogen-induced weak promoter impaired rice resistance.

Strategies for developing Green Super Rice

“…For example, Xa26 was isolated from the indica cultivar Minghui 63 (58), where it confers moderate resistance against bacterial blight at seedling and adult stages. When this gene was introduced into several japonica cultivars with its native promoter, transgenic plants showed enhanced resistance, featuring broadened resistance spectrum and increased resistance level in extended growth stages (73). It was shown that the enhanced resistance is closely associated with the elevated expression of the gene.…”

Gene dosage and genetic background affect miraculin accumulation in transgenic tomato fruits

“…Scott et al (1998) have claimed that allelic composition and genetic background affect transgene expression and inheritance in white clover. Another study in rice showed that the expression pattern of Xa3/Xa26, which is a rice disease resistance gene, was affected by the genetic background (Cao et al 2007). The full effects of gene dosage and genetic background on transgene expression and translation remain to be elucidated.…”

Review Article: Molecular Mechanisms of Resistance to Potato virus X and Y in Potato

“…Nevertheless, significant induction of R gene expression during the plant defence response also occurs in certain cases (Yoshimura et al, 1998;Halterman et al, 2003;Levy et al, 2004;Gu et al, 2005;Cao et al, 2007;Mohr et al, 2010). There are examples of increasing the expression of an R gene converts HR to ER suggesting that the level of R protein regulates the strength of resistance to a virus.…”