Identification of glycosyltransferases involved in cell wall synthesis of wheat endosperm.

Plant cell walls are complex structures critical for plant fitness and valuable for human nutrition as dietary fiber and for industrial uses such as biofuel production. The cell wall polysaccharides in wheat endosperm consist of two major polymers, arabinoxylans and beta-glucans, as well as other minor components. Most of these polysaccharides are synthesized in the Golgi apparatus but the mechanisms underlying their synthesis have yet to be fully elucidated and only a few of the enzymes involved have been characterized. To identify actors involved in the wheat endosperm cell wall formation, we used a subcellular fractionation strategy to isolate Golgi-enriched fractions from endosperm harvested during active cell wall deposition. The proteins extracted from these Golgi-enriched fractions were analyzed by LC-MS/MS. We report the identification of 1135 proteins among which 64 glycosyltransferases distributed in 17 families. Their potential function in cell wall synthesis is discussed. In addition, we identified 63 glycosylhydrolases, some of which may be involved in cell wall remodeling. Several glycosyltransferases were validated by showing that when expressed as fusion proteins with a fluorescent reporter, they indeed accumulate in the Golgi apparatus. Our results provide new candidates potentially involved in cell wall biogenesis in wheat endosperm.

Microsatellite mapping of Ae. speltoides and map-based comparative analysis of the S, G, and B genomes of Triticeae species.

The first microsatellite linkage map of Ae. speltoides Tausch (2n = 2x = 14, SS), which is a wild species with a genome closely related to the B and G genomes of polyploid wheats, was developed based on two F(2) mapping populations using microsatellite (SSR) markers from Ae. speltoides, wheat genomic SSRs (g-SSRs) and EST-derived SSRs. A total of 144 different microsatellite loci were mapped in the Ae. speltoides genome. The transferability of the SSRs markers between the related S, B, and G genomes allowed possible integration of new markers into the T. timopheevii G genome chromosomal maps and map-based comparisons. Thirty-one new microsatellite loci assigned to the genetic framework of the T. timopheevii G genome maps were composed of wheat g-SSR (genomic SSR) markers. Most of the used Ae. speltoides SSRs were mapped onto chromosomes of the G genome supporting a close relationship between the G and S genomes. Comparative microsatellite mapping of the S, B, and G genomes demonstrated colinearity between the chromosomes within homoeologous groups, except for intergenomic T6A(t)S.1G, T4AL.5AL.7BS translocations. A translocation between chromosomes 2 and 6 that is present in the T. aestivum B genome was found in neither Ae. speltoides nor in T. timopheevii. Although the marker order was generally conserved among the B, S, and G genomes, the total length of the Ae. speltoides chromosomal maps and the genetic distances between homoeologous loci located in the proximal regions of the S genome chromosomes were reduced compared with the B, and G genome chromosomes.

Characterization of the major fragance gene from an aromatic japonica rice and analysis of its diversity in Asian cultivated rice.

In Asian cultivated rice (Oryza sativa L.), aroma is one of the most valuable traits in grain quality and 2-ACP is the main volatile compound contributing to the characteristic popcorn-like odour of aromatic rices. Although the major locus for grain fragrance (frg gene) has been described recently in Basmati rice, this gene has not been characterised in true japonica varieties and molecular information available on the genetic diversity and evolutionary origin of this gene among the different varieties is still limited. Here we report on characterisation of the frg gene in the Azucena variety, one of the few aromatic japonica cultivars. We used a RIL population from a cross between Azucena and IR64, a non-aromatic indica, the reference genomic sequence of Nipponbare (japonica) and 93-11 (indica) as well as an Azucena BAC library, to identify the major fragance gene in Azucena. We thus identified a betaine aldehyde dehydrogenase gene, badh2, as the candidate locus responsible for aroma, which presented exactly the same mutation as that identified in Basmati and Jasmine-like rices. Comparative genomic analyses showed very high sequence conservation between Azucena and Nipponbare BADH2, and a MITE was identified in the promotor region of the BADH2 allele in 93-11. The badh2 mutation and MITE were surveyed in a representative rice collection, including traditional aromatic and non-aromatic rice varieties, and strongly suggested a monophylogenetic origin of this badh2 mutation in Asian cultivated rices. Altogether these new data are discussed here in the light of current hypotheses on the origin of rice genetic diversity.