Studying NB-LRR immune receptor localization by agroinfiltration transient expression

An improved and efficient method of Agrobacterium syringe infiltration for transient transformation and its application in the elucidation of gene function in poplar

BACKGROUND

Forest trees have important economic and ecological value. As a model tree, poplar has played a significant role in elucidating the molecular mechanisms underlying tree biology. However, a lack of mutant libraries and time-consuming stable genetic transformation processes severely limit progress into the functional characterization of poplar genes. A convenient and fast transient transformation method is therefore needed to enhance progress on functional genomics in poplar.

METHODS

A total of 11 poplar clones were screened for amenability to syringe infiltration. Syringe infiltration was performed on the lower side of the leaves of young soil-grown plants. Transient expression was evaluated by visualizing the reporters β-glucuronidase (GUS) and green fluorescent protein (GFP). The experimental parameters of the syringe agroinfiltration were optimized based on the expression levels of the reporter luciferase (LUC). Stably transformed plants were regenerated from transiently transformed leaf explants through callus-induced organogenesis. The functions of Populus genes in secondary cell wall-thickening were characterized by visualizing lignin deposition therein after staining with basic fuchsin.

RESULTS

We greatly improved the transient transformation efficiency of syringe Agrobacterium infiltration in poplar through screening for a suitable poplar clone from a variety of clones and optimizing the syringe infiltration procedure. The selected poplar clone, Populus davidiana × P. bolleana, is amenable to Agrobacterium syringe infiltration, as indicated by the easy diffusion of the bacterial suspension inside the leaf tissues. Using this technique, we localized a variety of poplar proteins in specific intracellular organelles and illustrated the protein-protein and protein-DNA interactions. The transiently transformed leaves could be used to generate stably transformed plants with high efficiency through callus induction and differentiation processes. Furthermore, transdifferentiation of the protoxylem-like vessel element and ectopic secondary wall thickening were induced in the agroinfiltrated leaves via the transient overexpression of genes associated with secondary wall formation.

CONCLUSIONS

The application of P. davidiana × P. bolleana in Agrobacterium syringe infiltration provides a foundation for the rapid and high-throughput functional characterization of Populus genes in intact poplar plants, including those involved in wood formation, and provides an effective alternative to Populus stable genetic transformation.

A draft genome sequence of Nicotiana benthamiana to enhance molecular plant-microbe biology research

Nicotiana benthamiana is a widely used model plant species for the study of fundamental questions in molecular plant-microbe interactions and other areas of plant biology. This popularity derives from its well-characterized susceptibility to diverse pathogens and, especially, its amenability to virus-induced gene silencing and transient protein expression methods. Here, we report the generation of a 63-fold coverage draft genome sequence of N. benthamiana and its availability on the Sol Genomics Network for both BLAST searches and for downloading to local servers. The estimated genome size of N. benthamiana is 3 Gb (gigabases). The current assembly consists of approximately 141,000 scaffolds, spanning 2.6 Gb with 50% of the genome sequence contained within scaffolds >89 kilobases. Of the approximately 16,000 N. benthamiana unigenes available in GenBank, >90% are represented in the assembly. The usefulness of the sequence was demonstrated by the retrieval of N. benthamiana orthologs for 24 immunity-associated genes from other species including Ago2, Ago7, Bak1, Bik1, Crt1, Fls2, Pto, Prf, Rar1, and mitogen-activated protein kinases. The sequence will also be useful for comparative genomics in the Solanaceae family as shown here by the discovery of microsynteny between N. benthamiana and tomato in the region encompassing the Pto and Prf genes.