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UDP-glucose 4-epimerase (UGE) catalyzes the reversible conversion of UDP-glucose to UDP-galactose. To understand the biological function of UGE from Brassica rapa, the gene BrUGE1 was cloned and introduced into the genome of wild type rice 'Gopum' using the Agrobacterium-mediated transformation method. Four lines which carried a single copy gene were selected and forwarded to T3 generation. Agronomic traits evaluation of the transgenic T3 lines (CB01, CB03, and CB06) under optimal field conditions revealed enriched biomass production particularly in panicle length, number of productive tillers, number of spikelets per panicle, and filled spikelets. These remarkably improved agronomic traits were ascribed to a higher photosynthetic rate complemented with higher CO2 assimilation. Transcripts of BrUGE1 in transgenic lines continuously accumulated at higher levels after the 20% PEG6000 treatment, implying its probable role in drought stress regulation. This was paralleled by rapid accumulation of soluble sugars which act as osmoprotectants, leading to delayed leaf rolling and drying. Our findings suggest the potential of BrUGE1 in improving rice growth performance under optimal and water deficit conditions.

To employ molecular marker-aided selection for developing japonica rice (Oryza sativa L.) cultivars with high yielding potential and good eating quality, we carried out QTL analysis for agronomic and grain traits using 231 recombinant inbred lines (RIL) from a cross between two temperate japonica cultivars, Suweon365 and Chucheongbyeo. A linkage map with 221 loci, including 134 simple sequence repeats (SSRs), 66 amplified fragment length polymorphisms (AFLPs), and 21 miniature inverted repeat transposable elements (MITEs)-anchored markers, was constructed covering 2,227 cM of the twelve rice chromosomes, with an average distance of 11.0 cM between markers. The proportion of polymorphic bands between parents averaged 19.5%, 12.9% and 42.3% for SSRs, AFLPs and MITEs, respectively. Construction of maps without AFLP or MITE markers indicated that expansion of this map is due to the incorporation of AFLP markers, and this result is consistent with previous reports. Twenty-seven QTLs for ten traits were identified over two years, and fourteen were consistently detected in two consecutive years. When the locations of each QTL detected in this study were compared with those in previous QTLs studies, eight QTLs for culm length, spikelets per panicle and, thickness, length and shape of grain, had not been reported in previous mapping studies, indicating potentially novel alleles of japonica rice. Interestingly, a cluster of seven QTLs, including heading date and grain morphology traits, was detected on the long arm of chromosome 7. The markers linked to these QTLs would be valuable in a marker-assisted breeding program for japonica cultivars.