RESUMO
Floods impede gas (O2 and CO2 ) exchange between plants and the environment. A mechanism to enhance plant gas exchange under water comprises gas films on hydrophobic leaves, but the genetic regulation of this mechanism is unknown. We used a rice mutant (dripping wet leaf 7, drp7) which does not retain gas films on leaves, and its wild-type (Kinmaze), in gene discovery for this trait. Gene complementation was tested in transgenic lines. Functional properties of leaves as related to gas film retention and underwater photosynthesis were evaluated. Leaf Gas Film 1 (LGF1) was identified as the gene determining leaf gas films. LGF1 regulates C30 primary alcohol synthesis, which is necessary for abundant epicuticular wax platelets, leaf hydrophobicity and gas films on submerged leaves. This trait enhanced underwater photosynthesis 8.2-fold and contributes to submergence tolerance. Gene function was verified by a complementation test of LGF1 expressed in the drp7 mutant background, which restored C30 primary alcohol synthesis, wax platelet abundance, leaf hydrophobicity, gas film retention, and underwater photosynthesis. The discovery of LGF1 provides an opportunity to better understand variation amongst rice genotypes for gas film retention ability and to target various alleles in breeding for improved submergence tolerance for yield stability in flood-prone areas.
Assuntos
Adaptação Fisiológica , Inundações , Gases/metabolismo , Genes de Plantas , Interações Hidrofóbicas e Hidrofílicas , Oryza/genética , Folhas de Planta/fisiologia , Ceras/metabolismo , Sequência de Bases , Vias Biossintéticas , Teste de Complementação Genética , Mutação/genética , Oryza/fisiologia , Fotossíntese , Epiderme Vegetal/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismoRESUMO
Rho family small GTPases are involved in diverse signaling processes including immunity, growth, and development. The activity of Rho GTPases is regulated by cycling between guanosine diphosphate (GDP)-bound inactive and guanosine triphosphate (GTP)-bound active forms, in which guanine nucleotide exchange factors (GEFs) predominantly function to promote activation of the GTPases. In animals, most Rho GEFs possess a Dbl (diffuse B-cell lymphoma) homology (DH) domain which functions as a GEF-catalytic domain. However, no proteins with the DH domain have been identified in plants so far. Instead, plant-specific Rho GEFs with the PRONE domain responsible for GEF activity have been found to constitute a large family in plants. In this study, we found rice homologs of human SWAP70, Oryza sativa (Os) SWAP70A and SWAP70B, containing the DH domain. OsSWAP70A interacted with rice Rho GTPase OsRac1, an important signaling factor for immune responses. The DH domain of OsSWAP70A exhibited the GEF-catalytic activity toward OsRac1 as found in animal Rho GEFs, indicating that plants have the functional DH domains. Transient expression of OsSWAP70A enhanced OsRac1-mediated production of reactive oxygen species in planta. Reduction of OsSWAP70A and OsSWAP70B mRNA levels by RNA interference resulted in the suppression of chitin elicitor-induced defense gene expression and ROS production. Thus, it is likely that OsSWAP70 regulates immune responses through activation of OsRac1.
Assuntos
Fatores de Troca do Nucleotídeo Guanina/genética , Oryza/genética , Imunidade Vegetal/genética , Sequência de Aminoácidos , Expressão Gênica/genética , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Dados de Sequência Molecular , Oryza/imunologia , Oryza/metabolismo , Filogenia , Folhas de Planta/genética , Folhas de Planta/imunologia , Folhas de Planta/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Mapeamento de Interação de Proteínas , Estrutura Terciária de Proteína , Interferência de RNA , RNA Mensageiro/genética , RNA de Plantas/genética , Espécies Reativas de Oxigênio/análise , Espécies Reativas de Oxigênio/metabolismo , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Transdução de Sinais , Nicotiana/genética , Nicotiana/metabolismo , Proteínas rac de Ligação ao GTP/genética , Proteínas rac de Ligação ao GTP/metabolismo , Proteínas rho de Ligação ao GTP/genética , Proteínas rho de Ligação ao GTP/metabolismoRESUMO
A lesion mimic mutant that we designated Spotted leaf 18 (Spl18) was isolated from 13,000 activation-tagging lines of rice produced by our modified activation-tagging vector and further characterized. Spl18 was dominant and its phenotype was linked to the T-DNA insertion. An ORF was located about 500 bp downstream of the inserted T-DNA, and the deduced protein, designated OsAT1, showed sequence similarity to an acyltransferase whose expression is induced by hypersensitive reaction in tobacco. The transcriptional level of OsAT1 was very low in the WT leaf blade but high in Spl18 leaf blade. In wild-type rice, OsAT1 was transcribed mainly in the young panicle, in the panicle just after heading, and in the leaf sheath. In addition, transcription of the genes for PR protein was upregulated in Spl18, accumulation of phytoalexins (both momilactone A and sakuranetin) was increased, and resistance to blast disease was improved. We then combined OsAT1 genomic DNA downstream of the modified 35S promoter and re-transformed it into rice. Lesion mimic and blast resistance phenotypes were detected in the transgenic lines produced, clearly indicating that overexpression of OsAT1 caused the Spl18 phenotypes. In addition, plants overexpressing OsAT1 showed resistance to bacterial blight.