Seasonal variation of western white pine (Pinus monticola D. Don) foliage proteins

Evidence for conifer sucrose transporters' functioning in the light-dependent adjustment of sugar allocation

Sucrose is the central unit of carbon and energy in plants. Active intercellular transport of sucrose is mediated by sucrose transporters (SUTs), genes for which have been found in the genomes of all land plants. However, they have only been assigned functions in angiosperm species. Here, we cloned two types of SUTs from two gymnosperms, the conifers Cedrus deodara (Roxb. G. Don) and Pinus massoniana Lambert, and analyzed their sucrose transport activities. Uptake of the fluorescent sucrose-analog esculin into tobacco epidermis cells expressing the conifer SUT confirmed their transport ability. To determine their function in planta, we investigated their mRNA abundance in relation to photosynthesis and sugar levels in leaves, inner bark, wood and roots. Combined with measurements of protein abundance and immunolocalization of C. deodara SUTs, our results suggest a role for CdSUT1G and CdSUT2 in supporting phloem transport under varying environmental conditions. The implications of these findings regarding conifer physiology and SUT evolution are discussed.

Host-Pathogen Interactions in Douglas-Fir Seedlings Infected by Phellinus sulphurascens

ABSTRACT Several aspects of the host-pathogen interaction between Douglas-fir (Pseudotsuga menziesii) and the fungal pathogen Phellinus sulphurascens were investigated in an in vitro inoculation system using young seedlings and fungal mycelia. Light microscopy confirmed that P. sulphurascens mycelia can successfully penetrate host epidermal cells within 3 days postinoculation (dpi). Extensive fungal colonization and cortical cell decay occurred within 14 dpi. Western immunoblot studies showed significant upregulation (five to sixfold) of four specific pathogenesis-related (PR) proteins in infected roots. These proteins were a Douglas-fir thaumatin-like protein (PmTLP), an endochitinase protein (ECP), a Douglas-fir PR10 (DF-PR10) protein (PsemI), and a 10.6-kDa antimicrobial peptide (PmAMP1). The highest accumulation of PmTLP and PmAMP1 occurred at 12 dpi, whereas accumulations of the ECP and DF-PR10 proteins peaked at 7 dpi. For both inoculated and control Douglas-fir seedlings, only one of the four PR proteins, PmAMP1, was clearly detectable in needles. Immunolocalization experiments using fluorescein isothiocyanate-conjugated secondary antibodies confirmed accumulation of all four PR proteins mainly in and around cell walls of root cortical tissues. Overall, the highest immunofluorescence was observed in infected roots at 12 dpi, whereas labeling in control roots was negligible at all sample times. The ECP produced the highest fluorescence; the DF-PR10 the lowest. Upregulation and localization of these PR proteins in cortical tissues of inoculated roots suggest that they play a defensive role in response to infection by P. sulphurascens. This in vitro inoculation system will facilitate further proteomic and genomic studies of this important pathosystem.

Cloning and characterization of a cDNA of cro rI from the white pine blister rust fungus Cronartium ribicola

White pine blister rust (WPBR) is caused by the fungus Cronartium ribicola which has five spore stages on two unrelated hosts, the five-needle pines and Ribes spp. Recently, during the molecular analysis of the proteins and genes involved in host-pathogen interaction, the WPBR fungal protein Cro rI was identified in infected white pine tissues. To further characterize Cro rI, an expression cDNA library from poly(A)(+) mRNA of C. ribicola axenic mycelial culture was constructed and immunoscreened and the cDNA was cloned. Sequence analysis indicated an open reading frame of 462 bases, which encodes a protein of 153 amino acid residues with a molecular mass of 16.7 kDa and a predicted isoelectric point (pI) of 8.93. Based on the N-terminal amino acid sequences of Cro rI, the secreted portion of Cro rI protein should be 136 amino acids long with several putative posttranslational modification sites and a molecular mass of 14.8 kDa. The predicted pI for the secreted portion was 9.34. The predicted N-terminal signal peptide was 17 amino acids long. The N-terminal 42-amino acid sequence of the predicted mature protein (secreted portion) was identical to the amino terminal sequence of Cro rI that was previously determined. Southern blot hybridizations indicated that the C. ribicola genome contained at least two copies of the cro rI gene. Isolation of the genomic PCR fragment, which was approximately 400 bp longer than the cDNA, and subsequent cloning and sequencing analyses confirmed that there were three introns within the coding regions. Western immunoblot analyses revealed that Cro rI protein accumulated in large amounts only in the infected white pine tissues while no trace was detectable in the alternate Ribes stage or the five different spores, suggesting a critical role of Cro rI in the haploid stage of the fungus (in pine). The translocation of Cro rI was only found to occur in cankered trees, and not in the young infected seedlings. The implications of Cro rI in pathogenesis are discussed.