Maize unstable factor for orange1 is essential for endosperm development and carbohydrate accumulation.

Maize (Zea mays L.) Ufo1-1 is a spontaneous dominant mutation of the unstable factor for orange1 (ufo1). We recently cloned ufo1, which is a Poaceae-specific gene highly expressed during seed development in maize. Here, we have characterized Ufo1-1 and a loss-of-function Ds insertion allele (ufo1-Dsg) to decipher the role of ufo1 in maize. We found that both ufo1 mutant alleles impact sugars and hormones, and have defects in the basal endosperm transfer layer (BETL) and adjacent cell types. The Ufo1-1 BETL had reduced cell elongation and cell wall ingrowth, resulting in cuboidal shaped transfer cells. In contrast, the ufo1-Dsg BETL cells showed a reduced overall size with abnormal wall ingrowth. Expression analysis identified the impact of ufo1 on several genes essential for BETL development. The overexpression of Ufo1-1 in various tissues leads to ectopic phenotypes, including abnormal cell organization and stomata subsidiary cell defects. Interestingly, pericarp and leaf transcriptomes also showed that as compared with wild type, Ufo1-1 had ectopic expression of endosperm development-specific genes. This study shows that Ufo1-1 impacts the expression patterns of a wide range of genes involved in various developmental processes.

The Dominant and Poorly Penetrant Phenotypes of Maize Unstable factor for orange1 Are Caused by DNA Methylation Changes at a Linked Transposon.

The maize (Zea mays) mutant Unstable factor for orange1 (Ufo1) has been implicated in the epigenetic modifications of pericarp color1 (p1), which regulates the production of the flavonoid pigments phlobaphenes. Here, we show that the ufo1 gene maps to a genetically recalcitrant region near the centromere of chromosome 10. Transcriptome analysis of Ufo1-1 mutant and wild-type plants identified a candidate gene in the mapping region using a comparative sequence-based approach. The candidate gene, GRMZM2G053177, is overexpressed by >45-fold in multiple tissues of Ufo1-1, explaining the dominance of Ufo1-1 and its phenotypes. In the mutant stock, GRMZM2G053177 has a unique transcript originating within a CACTA transposon inserted in its first intron, and it is missing the first four codons of the wild-type transcript. GRMZM2G053177 expression is regulated by the DNA methylation status of the CACTA transposon, explaining the incomplete penetrance and poor expressivity of Ufo1-1 Transgenic overexpression lines of GRMZM2G053177 (Ufo1-1) phenocopy the p1-induced pigmentation in coleoptiles, tassels, leaf sheaths, husks, pericarps, and cob glumes. Transcriptome analysis of Ufo1 versus wild-type tissues revealed changes in several pathways related to abiotic and biotic stress. Thus, this study addresses the enigma of Ufo1 identity in maize, which had gone unsolved for more than 50 years.

Resynthesis of Brassica napus through hybridization between B. juncea and B. carinata.

KEY MESSAGE: First report for the resynthesis of Brassica napus by recombining A and C genome from B. juncea and B. carinata , respectively. Also documents B genome introgressions in resynthesized B. napus. Resynthesis of Brassica napus (AACC) was achieved by hybridizing Brassica juncea (AABB) with Brassica carinata (BBCC). This was facilitated by spontaneous chromosome doubling in the F1 hybrid (ABBC) to yield octaploid (AABBBBCC), elimination of extra B genome chromosomes in the resulting octaploid and in subsequent selfed generations, aided with directed selection for fertile plants having B. napus morphology. Twenty-five plants with varying degrees of resemblance to natural B. napus were identified from 17 A5 progenies and assayed for cytogenetic stability and genetic diversity. Majority of these plants, except six (2n = 38) were hyperploids (2n = 40-56). The six plants with 2n = 38 were designated as derived B. napus types. These showed an expected meiotic configuration of 19II at metaphase-I, with 19-19 distribution at anaphase-I. Genotyping based on A and C genome specific primers confirmed genetic identity of six derived (2n = 38) B. napus plants with natural types whereas genotyping with B genome specific primers indicated introgression of B genome segments. This was also confirmed by genomic in situ hybridization (GISH). Strong signals of B genome probe were detected, proving hitherto unreported genetic exchanges between B and A/C chromosomes. These introgressions possibly occurred en route five generations of selfing. Derived plants yielded fertile hybrids in crosses with natural B. napus var. GSC 6. The selfed derived plants as evaluated in A6 plant to progeny rows were morphologically similar to natural B. napus, and meiotically stable. Agronomic assessment of these progenies revealed variation for key morpho-physiological traits. Of special interest were the progenies with plants having oil content exceeding 47% as against about 39-41% in existing cultivars.