Response of tomatoes primed by mycorrhizal colonization to virulent and avirulent bacterial pathogens.

Most plants interact with arbuscular mycorrhizal fungi, which enhance disease resistance in the host plant. Because the effects of resistance against bacterial pathogens are poorly understood, we investigated the effects of mycorrhizal colonization on virulent and avirulent pathogens using phytopathological and molecular biology techniques. Tomato plants colonized by Gigaspora margarita acquired resistance not only against the fungal pathogen, Botrytis cinerea, but also against a virulent bacterial pathogen, Pseudomonas syringae pv.

Rice transgenic plants with suppressed expression of the β subunit of the heterotrimeric G protein.

The deficient mutant for the rice heterotrimeric G protein α subunit gene (RGA1), d1, showed dwarfism and set small seed due to a reduced cell number. Mutants for the rice heterotrimeric G protein β subunit gene (RGB1) have not been isolated. To determine the functions of RGB1, transgenic rice plants with suppressed expression of RGB1 were studied using the RNAi method.

Suppression of the rice heterotrimeric G protein β-subunit gene, RGB1, causes dwarfism and browning of internodes and lamina joint regions.

In the present study, we investigated the function of the heterotrimeric G protein β-subunit (Gβ) gene (RGB1) in rice. RGB1 knock-down lines were generated in the wild type and d1-5, a mutant deficient for the heterotrimeric G protein α-subunit (Gα) gene (RGA1). Both transgenic lines showed browning of the lamina joint regions and nodes that could be attributed to a reduction of RGB1 function, as the abnormality was not observed in d1-5.

Function and expression pattern of the alpha subunit of the heterotrimeric G protein in rice.

The d1 mutant, which is deficient for the heterotrimeric G-protein alpha subunit (Galpha) gene of rice, shows dwarfism and sets small round seeds. To determine whether dwarfism in d1 is due to a reduction in cell number or to shortened cell length, the cell number of the leaf sheath, the internode, the root and the lemma was compared between Nipponbare, a wild-type rice and d1-5, a d1 allele derived from Nipponbare. Our results indicate that the cell number was reduced in all organs analyzed in d1-5.

Function of alpha subunit of heterotrimeric G protein in brassinosteroid response of rice plants.

The alpha subunit of heterotrimeric G-proteins (G alpha) is involved in a broad range of aspects of the brassinosteroid (BR) response, such as the enhancement of lamina bending. However, it has been suggested from epistatic analysis of d1 and d61, which are mutants deficient for G alpha and the BR receptor BRI1, that G alpha and BRI1 may function via distinct pathways in many cases. In this study, we investigated further the genetic interaction between G alpha and BRI1.

Study of novel d1 alleles, defective mutants of the alpha subunit of heterotrimeric G-protein in rice.

It has been shown that the disruption of the alpha-subunit gene of heterotorimeric G-proteins (Galpha) results in dwarf traits, the erection of leaves and the setting of small seeds in rice. These mutants are called d1. We have studied the expression profiles of the transcripts and translation products of rice Galpha in ten alleles of d1 including five additional alleles newly identified.

Function of the alpha subunit of rice heterotrimeric G protein in brassinosteroid signaling.

The alpha subunit of plant heterotrimeric G proteins (Galpha) plays pivotal roles in multiple aspects of development and responses to plant hormones. Recently, several lines of evidence have shown that Galpha participates in brassinosteroid (BR) responses in Arabidopsis and rice plants. In this study, we conducted a comprehensive analysis of the roles of the rice Galpha in the responses to BR using a defective mutant of the Galpha gene, T65d1.

Proteomic analysis of rice embryo: an approach for investigating Galpha protein-regulated proteins.

The rice dwarf1 (d1) mutant, which lacks the alpha subunit of a heterotrimeric G protein (Galpha protein), shows abnormal morphology due to shortened internodes, dark green leaves and grains that are small and round. Proteome analysis was used in this study to aid in determining the function of Galpha protein in rice embryos. Using 2-DE, seven seed embryo proteins were shown to be down-regulated in the d1 mutant as compared with its wild type.

A novel cytochrome P450 is implicated in brassinosteroid biosynthesis via the characterization of a rice dwarf mutant, dwarf11, with reduced seed length.

We have characterized a rice (Oryza sativa) dwarf mutant, dwarf11 (d11), that bears seeds of reduced length. To understand the mechanism by which seed length is regulated, the D11 gene was isolated by a map-based cloning method. The gene was found to encode a novel cytochrome P450 (CYP724B1), which showed homology to enzymes involved in brassinosteroid (BR) biosynthesis.

Study of the constitutively active form of the alpha subunit of rice heterotrimeric G proteins.

We used site-directed mutagenesis to engineer two constitutively active forms of the alpha subunit of a rice heterotrimeric G protein. The recombinant proteins produced from these novel cDNAs had GTP-binding activity but no GTPase activity. A chimeric gene for a constitutively active form of the alpha subunit was introduced into the rice mutant d1, which is defective for the alpha-subunit gene.

Characterization of heterotrimeric G protein complexes in rice plasma membrane.

Two genes in the rice genome were identified as those encoding the gamma subunits, gamma1 and gamma2, of heterotrimeric G proteins. Using antibodies against the recombinant proteins for the alpha, beta, gamma1, and gamma2 subunits of the G protein complexes, all of the subunits were proven to be localized in the plasma membrane in rice. Gel filtration of solubilized plasma membrane proteins showed that all of the alpha subunits were present in large protein complexes (about 400 kDa) containing the other subunits, beta, gamma1, and gamma2, and probably also some other proteins, whereas large amounts of the beta and gamma (gamma1 and gamma2) subunits were freed from the large complexes and took a 60-kDa form.