Characterization of a family of Arabidopsis genes related to xyloglucan fucosyltransferase1

Inducible expression of Pisum sativum xyloglucan fucosyltransferase in the pea root cap meristem, and effects of antisense mRNA expression on root cap cell wall structural integrity

Mitosis and cell wall synthesis in the legume root cap meristem can be induced and synchronized by the nondestructive removal of border cells from the cap periphery. Newly synthesized cells can be examined microscopically as they differentiate progressively during cap development, and ultimately detach as a new population of border cells. This system was used to demonstrate that Pisum sativum L. fucosyl transferase (PsFut1) mRNA expression is strongly expressed in root meristematic tissues, and is induced >2-fold during a 5-h period when mitosis in the root cap meristem is increased. Expression of PsFut1 antisense mRNA in pea hairy roots under the control of the CaMV35S promoter, which exhibits meristem localized expression in pea root caps, resulted in a 50-60% reduction in meristem localized endogenous PsFut1 mRNA expression measured using whole mount in situ hybridization. Changes in gross levels of cell wall fucosylated xyloglucan were not detected, but altered surface localization patterns were detected using whole mount immunolocalization with CCRC-M1, an antibody that recognizes fucosylated xyloglucan. Emerging hairy roots expressing antisense PsFut1 mRNA appeared normal macroscopically but scanning electron microscopy of tissues with altered CCRC-M1 localization patterns revealed wrinkled, collapsed cell surfaces. As individual border cells separated from the cap periphery, cell death occurred in correlation with extrusion of cellular contents through breaks in the wall.

Microarray analysis of flax (Linum usitatissimum L.) stems identifies transcripts enriched in fibre-bearing phloem tissues

To better understand the molecular processes associated with the development of the unusually long (> 30 mm) and strong bast fibre cells within the phloem of flax stems, we conducted a gene discovery experiment to identify transcripts enriched in fibre-bearing tissues, with the intention that these transcripts would serve as future targets for crop improvement and research in phloem development and cell wall deposition. We produced a library of 9,600 cDNA clones from the peels of flax stems, and selected tissue-specific cDNAs for sequencing based on two series of microarray experiments. In the first microarray series, we compared transcript abundance in stem-peels and leaves, and identified stem-enriched transcripts putatively involved in the processes of polysaccharide and cell wall metabolism. In the second microarray series, we compared gene expression in three segments of the vertical stem axis, which constituted a developmental series for phloem fibres and other cell types. The expression of specific LTP and AGP transcripts was particularly well-correlated with stem segments during either the elongation phase or cell-wall thickening phase of phloem fibre development, and the phloem-specific enrichment of these transcripts was confirmed by qRT-PCR. Transcripts representing multiple, distinct chitinases, beta-galactosidases, arabinogalactan proteins (AGP), and lipid transfer proteins (LTPs) were among the interesting transcripts enriched in specific stages of the developing stem. Considered together, the results of our analyses suggest similarity between the molecular mechanisms underlying phloem fibre development and the gelatinous fibres of tension wood in trees.

Opportunities to improve fiber degradation in the rumen: microbiology, ecology, and genomics

The degradation of plant cell walls by ruminants is of major economic importance in the developed as well as developing world. Rumen fermentation is unique in that efficient plant cell wall degradation relies on the cooperation between microorganisms that produce fibrolytic enzymes and the host animal that provides an anaerobic fermentation chamber. Increasing the efficiency with which the rumen microbiota degrades fiber has been the subject of extensive research for at least the last 100 years. Fiber digestion in the rumen is not optimal, as is supported by the fact that fiber recovered from feces is fermentable. This view is confirmed by the knowledge that mechanical and chemical pretreatments improve fiber degradation, as well as more recent research, which has demonstrated increased fiber digestion by rumen microorganisms when plant lignin composition is modified by genetic manipulation. Rumen microbiologists have sought to improve fiber digestion by genetic and ecological manipulation of rumen fermentation. This has been difficult and a number of constraints have limited progress, including: (a) a lack of reliable transformation systems for major fibrolytic rumen bacteria, (b) a poor understanding of ecological factors that govern persistence of fibrolytic bacteria and fungi in the rumen, (c) a poor understanding of which glycolyl hydrolases need to be manipulated, and (d) a lack of knowledge of the functional genomic framework within which fiber degradation operates. In this review the major fibrolytic organisms are briefly discussed. A more extensive discussion of the enzymes involved in fiber degradation is included. We also discuss the use of plant genetic manipulation, application of free-living lignolytic fungi and the use of exogenous enzymes. Lastly, we will discuss how newer technologies such as genomic and metagenomic approaches can be used to improve our knowledge of the functional genomic framework of plant cell wall degradation in the rumen.