Abstract
Breeding crops with the quality of broad-spectrum disease resistance using genetic resources is one of the principal goals of crop improvement. However, the molecular mechanism of broad-spectrum resistance remains largely unknown. Here, we show that GH3-2, encoding an indole-3-acetic acid (IAA)-amido synthetase, mediates a broad-spectrum resistance to bacterial Xanthomonas oryzae pv oryzae and Xanthomonas oryzae pv oryzicola and fungal Magnaporthe grisea in rice (Oryza sativa). IAA, the major form of auxin in rice, results in rice more vulnerable to the invasion of different types of pathogens, which is at least partly due to IAA-induced loosening of the cell wall, the natural protective barrier of plant cells to invaders. X. oryzae pv oryzae, X. oryzae pv oryzicola, and M. grisea secrete IAA, which, in turn, may induce rice to synthesize its own IAA at the infection site. IAA induces the production of expansins, the cell wall-loosening proteins, and makes rice vulnerable to pathogens. GH3-2 is likely contributing to a minor quantitative trait locus for broad-spectrum resistance. Activation of GH3-2 inactivates IAA by catalyzing the formation of an IAA-amino acid conjugate, which results in the suppression of expansin genes. Thus, GH3-2 mediates basal resistance by suppressing pathogen-induced IAA accumulation. It is expected that, regulated by a pathogen-induced strong promoter, GH3-2 alone may be used for breeding rice with a broad-spectrum disease resistance.
Highlights
Breeding crops with the quality of broad-spectrum disease resistance using genetic resources is one of the principal goals of crop improvement
To ascertain whether GH3-2 played a role in ricepathogen interactions, we performed functional complementary and QTL analyses of GH3-2. These analyses suggest that GH3-2 encodes an indole-3-acetic acid (IAA)-amido synthetase and may contribute to a minor resistance QTL
We mapped GH3-2 in a recombinant inbred line (RIL) segregation population that was developed from a cross between Zhenshan 97 and Minghui 63
Summary
Breeding crops with the quality of broad-spectrum disease resistance using genetic resources is one of the principal goals of crop improvement. IAA, the major form of auxin in rice, results in rice more vulnerable to the invasion of different types of pathogens, which is at least partly due to IAA-induced loosening of the cell wall, the natural protective barrier of plant cells to invaders. Quantitative resistance is presumably nonspecific for pathogen species or race and is, durable It is the only type of resistance for some. Plants have evolved a wide variety of effective ways to regulate IAA homeostasis, one of which is to conjugate IAA to other molecules such as amino acids, sugars, peptides, or even proteins to activate or inactivate it (Seidel et al, 2006; Bari and Jones, 2009; Ludwig-Muller et al, 2009). Some GH3 proteins are IAA-, SA-, or jasmonic acid (JA)-amido synthetases, which modify the action of IAA, SA, or JA by conjugating them to amino acids (Staswick et al, 2005; Ludwig-Muller et al, 2009)
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