Soybean [Glycine max (L.) Merril], one of the most important crop species in the world, is very susceptible to abiotic and biotic stress. Soybean plants have developed a variety of molecular mechanisms that help them survive stressful conditions. Hybrid proline-rich proteins (HyPRPs) constitute a family of cell-wall proteins with a variable N-terminal domain and conserved C-terminal domain that is phylogenetically related to non-specific lipid transfer proteins. Members of the HyPRP family are involved in basic cellular processes and their expression and activity are modulated by environmental factors. In this study, microarray analysis and real time RT-qPCR were used to identify putative HyPRP genes in the soybean genome and to assess their expression in different plant tissues. Some of the genes were also analyzed by time-course real time RT-qPCR in response to infection by Phakopsora pachyrhizi, the causal agent of Asian soybean rust disease. Our findings indicate that the time of induction of a defense pathway is crucial in triggering the soybean resistance response to P. pachyrhizi. This is the first study to identify the soybean HyPRP group B family and to analyze disease-responsive GmHyPRP during infection by P. pachyrhizi.

Transgenic plants represent an invaluable tool for molecular, genetic, biochemical and physiological studies by gene overexpression or silencing, transposon-based mutagenesis, protein sub-cellular localization and/or promoter characterization as well as a breakthrough for breeding programs, allowing the production of novel and genetically diverse genotypes. However, the stable transformation of soybean cannot yet be considered to be routine because it depends on the ability to combine efficient transformation and regeneration techniques. Two methods have been used with relative success to produce completely and stably transformed plants: particle bombardment and the Agrobacterium tumefaciens system. In addition, transformation by Agrobacterium rhizogenes has been used as a powerful tool for functional studies. Most available information on gene function is based on heterologous expression systems. However, as the activity of many promoters or proteins frequently depends on specific interactions that only occur in homologous backgrounds, a final confirmation based on a homologous expression system is desirable. With respect to soybean biotech improvement, transgenic lines with agronomical, nutritional and pharmaceutical traits have been obtained, including herbicide-tolerant soybeans, which represented the principal biotech crop in 2011, occupying 47% of the global biotech area.

O objetivo deste trabalho foi realizar a triagem de genótipos de soja quanto à sua habilidade de resposta à indução de raízes fasciculadas por transformação mediada por Agrobacterium rhizogenes. Quatro cultivares brasileiras de soja (BRSMG 68 Vencedora, BRS 137, Embrapa 48 e MG/BR 46 Conquista) e duas norte americanas, adaptadas às condições brasileiras de cultivo (Bragg e IAS‑5), foram avaliadas quanto à sua capacidade de responder a A. rhizogenes, em protocolos de cultura de raízes fasciculadas in vitro e de produção ex vitro de plantas compostas. Plântulas com quatro dias de idade, de tamanho uniforme, foram injetadas com A. rhizogenes portando o plasmídeo p35S‑GFP. As plântulas que expressaram a proteína verde fluorescente (GFP) em pelo menos uma raiz foram utilizadas para determinar a frequência de transformação. Utilizando um protocolo de obtenção de raízes axênicas, in vitro, cotilédones excisados de plântulas com quatro dias de idade foram infectados com A. rhizogenes portando o plasmídeo pCAMBIA1301 contendo o gene repórter gusA. Foram avaliados a frequência de transformação e o número de dias para emergência das raízes fasciculadas após a infecção bacteriana (DAI). A frequência de transformação e o DAI variaram conforme o genótipo. As cultivares MG/BR 46 Conquista e BRSMG 68 Vencedora são mais suscetíveis a A. rhizogenes e podem ser recomendadas para experimentos de transformação.

The objective of this work was to perform the screening of soybean genotypes as to their ability to respond to the induction of hairy roots by Agrobacterium rhizogenes‑mediated transformation. Four Brazilian soybean cultivars (BRSMG 68 Vencedora, BRS 137, Embrapa 48, and MG/BR 46 Conquista) and two North American ones adapted to Brazilian cropping conditions (Bragg and IAS‑5) were screened for their capacity to respond to A. rhizogenes in protocols for in vitro hairy root culture and ex vitro composite plant production. Four‑day‑old seedlings with uniform size were injected with A. rhizogenes harboring the plasmid p35S‑GFP. Seedlings expressing green fluorescent protein (GFP) in at least one hairy root were used to determine the transformation frequency. Using an axenic in vitro protocol, excised cotyledons from four‑day‑old seedlings were infected with A. rhizogenes harboring the pCAMBIA1301 plasmid, containing the gusA reporter gene. The transformation frequency and the number of days for hairy root emergence after bacterial infection (DAI) were evaluated. The transformation frequency and DAI varied according to the genotype. Cultivars MG/BR 46 Conquista and BRSMG 68 Vencedora are more susceptible to A. rhizogenes and can be recommended for transformation experiments.