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Title: LrABCF1, a GCN-type ATP-binding cassette transporter from lilium regale, is involved in defense responses against viral and fungal pathogens

item SUN, DAOYANG - University Of California
item ZHANG, XINGUO - Northwest Agricultural & Forestry University
item LI, SHAOHUA - Northwest Agricultural & Forestry University
item Jiang, Cai-Zhong
item ZHANG, YANLONG - Northwest Agricultural & Forestry University
item NIU, LIXIN - Northwest Agricultural & Forestry University

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2016
Publication Date: 8/2/2016
Citation: Sun, D., Zhang, X., Li, S., Jiang, C., Zhang, Y., Niu, L. 2016. LrABCF1, a GCN-type ATP-binding cassette transporter from Lilium regale, is involved in defense responses against viral and fungal pathogens. Planta. 244(6):185-1199. doi: 10.1007/s00425-016-2576-5.

Interpretive Summary: ABC transporters form a large protein superfamily and play an active role in the transport of a variety of structurally unrelated components across membranes as well as in plant-pathogen interaction. In yeast and human, the GCN class ABC transporter is primarily responsible for down-regulation of protein synthesis by activating a subunit of eukaryotic translation initiation factor 2 (eIF2a) kinase. The eIF2a phosphorylation by GCN2 causes accelerated translation of GCN4, which acts as a transcription activator to induce hundreds of amino acids synthesis-associated genes expression in yeast. Evidences support that translational activator GCN3 positively regulates the expression of GCN4 under amino acid-starved conditions in yeast. In plant, however, the GCNs functions are just preliminarily characterized and demand further investigation. A total of 5 members have been identified in the GCN subfamily, which contains two NBFs without transmembrane spans, in Arabidopsis. AtGCN2 sequence is highly similar to its counterparts in yeast and mammalian genome, and likely contribute to the phosphorylation of eIF2a, bringing about substantial depression of protein synthesis. SCODR5, encoding an ABC protein AtGCN3, is involved in Arabidopsis plant defense against Pseudomonas syringae pv. tomato DC3000 infection presumably through control of stress-related protein translation in stomatal tissues. Other reports implicate the functional characterization of one principle histone acetyltransferase AtGCN5, whose mutant exhibits enhanced pleiotropic effects on Arabidopsis growth and decreased transcripts of 5% of genes. But little is known about the function of in planta GCN1, especially in response to viruses, fungi and other biotic stresses. Lilium, one of ten predominant flowers in the export market of whole world, displays high ornamental and economic values. Viral disease is considered to be one of limited factors for lily cultivation. Lily viruses directly transmitted by means of aphids and bulbs of successive propagation could rapidly spread to the entire planting areas. Particularly, CMV and LMoV are most widely epidemic, resulting in dwarf plants, mosaic leaves, distorted flowers, low bulb yield and other aberrations. A commonly used strategy concerning the virus-free propagation materials has proved to be not fully effective to control virus. Therefore, molecular genetic manipulation is a promising approach to generate virus-resistant transgenic lily plants, despite the general recalcitrance of monocotyledons to genetic transformation. One of the examples is that Lilium cv Acapulco shows enhanced resistance to CMV when introduced with a defective CMV replicase gene. Apart from virus, the fungal pathogen B. cinerea commonly occurs in floral tissues of Lilium and severely impairs its ornamental trait. A total of 55 wild species and 32 cultivated varieties of Lilium are distributed in China, occupying about half of world species, and 11 species have been found in Chinese Qin-ba Mountains. L. regale, an endemic species native to China, is known as its desirable resistance in response to abiotic (drought) and biotic (fungi and viruses) stresses. We previously evaluated the variation of virus resistance in six wild Lilium species from Qin-ba Mountains under natural inoculation in field. Of all species tested, L. regale showed free infection by viruses over the course of growth, suggesting that it displayed excellent resistance to viral disease. In present study, a cluster of highly-expressed genes in L. regale seedling leaves infected by CMV were identified, including a GCN-type ABC transporter termed as LrABCF1. We found that transcript abundances of this gene were significantly up-regulated in leaves of 10 wild Lilium species inoculated with CMV and LMoV. Ectopic expression of LrABCF1 in petunia delayed the plant growth and development. Mor

Technical Abstract: ATP-binding cassette (ABC) transporters are essential for membrane translocation in diverse biological processes, such as plant development and defense response. Here, a general control non-derepressible (GCN)-type ABC transporter gene, designated LrABCF1, was identified from Cucumber mosaic virus (CMV)-induced cDNA library of L. regale. LrABCF1 was up-regulated upon inoculation with CMV and Lily mottle virus (LMoV). Salicylic acid (SA) and ethylene (ET) application and treatments with abiotic stresses such as cold, high salinity, and wounding increased the transcript abundances of LrABCF1. Constitutive overexpression of LrABCF1 in petunia (Petunia × hybrida) resulted in an impairment of plant growth and development. LrABCF1 overexpression conferred reduced susceptibility to CMV, Tobacco rattle virus (TRV), and B. cinerea infection in transgenic petunia plants, accompanying by elevated transcripts of PhGCN2 and a few defense-related genes in SA-signaling pathway. Our data indicate that LrABCF1 positively modulates viral and fungal resistance.