Victor Llaca

A phenylalanine in DGAT is a key determinant of oil content and composition in maize

Plant oil is an important renewable resource for biodiesel production and for dietary consumption by humans and livestock. Through genetic mapping of the oil trait in plants, studies have reported multiple quantitative trait loci (QTLs) with small effects, but the molecular basis of oil QTLs remains largely unknown. Here we show that a high-oil QTL (qHO6) affecting maize seed oil and oleic-acid contents encodes an acyl-CoA:diacylglycerol acyltransferase (DGAT1-2), which catalyzes the final step of oil synthesis. We further show that a phenylalanine insertion in DGAT1-2 at position 469 (F469) is responsible for the increased oil and oleic-acid contents. The DGAT1-2 allele with F469 is ancestral, whereas the allele without F469 is a more recent mutant selected by domestication or breeding. Ectopic expression of the high-oil DGAT1-2 allele increases oil and oleic-acid contents by up to 41% and 107%, respectively. This work provides insights into the molecular basis of natural variation of oil and oleic-acid contents in plants and highlights DGAT as a promising target for increasing oil and oleic-acid contents in other crops.

A Maize Glutaredoxin Gene, Abphyl2, Regulates Shoot Meristem Size and Phyllotaxy

A novel pathway, composed of a glutaredoxin and a TGA transcription factor, regulates shoot apical meristem size independently of CLV-WUS signaling. Phyllotaxy describes the geometric arrangement of leaves and is important for plant productivity. Auxin is well known to regulate phyllotactic patterns via PIN1-dependent auxin polar transport, and studies of maize (Zea mays) aberrant phyllotaxy1 (abph1) mutants suggest the importance of auxin and cytokinin signaling for control of phyllotaxy. However, whether additional regulators control these patterns is poorly understood. Here, we report a new dominant maize mutant, Aberrant phyllotaxy2 (Abph2), in which the shoot meristems are enlarged and the phyllotactic pattern switches from alternate to decussate. Map-based cloning revealed that the Abph2 mutation was caused by transposition of a glutaredoxin gene, MALE STERILE CONVERTED ANTHER1 (MSCA1), which gained an altered expression pattern in Abph2 mutant embryos. msca1 loss-of-function mutants have reduced meristem size and revealed a novel function of glutaredoxins in meristem growth. In addition, MSCA1 interacts with a TGA transcription factor, FASCIATED EAR4, suggesting a novel regulatory module for regulating shoot meristem size.

tassel-less1 Encodes a Boron Channel Protein Required for Inflorescence Development in Maize

tassel-less1 (tls1) is a classical maize (Zea mays) inflorescence mutant. Homozygous mutant plants have no tassels or very small tassels, and ear development is also impaired. Using a positional cloning approach, ZmNIP3;1 (a NOD26-like intrinsic protein) was identified as the candidate gene for tls1. The ZmNIP3;1 gene is completely deleted in the tls1 mutant genome. Two Mutator-insertional TUSC alleles of ZmNIP3;1 exhibited tls1-like phenotypes, and allelism tests confirmed that the tls1 gene encodes ZmNIP3;1. Transgenic plants with an RNA interference (RNAi) construct to down-regulate ZmNIP3;1 also showed tls1-like phenotypes, further demonstrating that TLS1 is ZmNIP3;1. Sequence analysis suggests that ZmNIP3;1 is a boron channel protein. Foliar application of boron could rescue the tls1 phenotypes and restore the normal tassel and ear development. Gene expression analysis indicated that in comparison with that of the wild type or tls1 plants treated with boron, the transition from the vegetative to reproductive phase or the development of the floral meristem is impaired in the shoot apical meristem of the tls1 mutant plants. It is concluded that the tls1 mutant phenotypes are caused by impaired boron transport, and boron is essential for inflorescence development in maize.

Sequencing and de novo draft assemblies of a fathead minnow (Pimephales promelas) reference genome

The present study was undertaken to provide the foundation for development of genome-scale resources for the fathead minnow (Pimephales promelas), an important model organism widely used in both aquatic toxicology research and regulatory testing. The authors report on the first sequencing and 2 draft assemblies for the reference genome of this species. Approximately 120× sequence coverage was achieved via Illumina sequencing of a combination of paired-end, mate-pair, and fosmid libraries. Evaluation and comparison of these assemblies demonstrate that they are of sufficient quality to be useful for genome-enabled studies, with 418 of 458 (91%) conserved eukaryotic genes mapping to at least 1 of the assemblies. In addition to its immediate utility, the present work provides a strong foundation on which to build further refinements of a reference genome for the fathead minnow.

Genome Diversity in Maize

Zea mays (maize) has historically been used as a model species for genetics, development, physiology and more recently, genome structure. The maize genome is complex with striking intraspecific variation in gene order, repetitive DNA content, and allelic content exceeding the levels observed between primate species. Maize genome complexity is primarily driven by polyploidization and explosive amplification of LTR retrotransposons, with the counteracting effect of unequal and illegitimate crossover. Transposable elements have been shown to capture genic content, create chimeras, and amplify those sequences via transposition. New sequencing platforms and hybridization-based strategies have appeared over the past decade which are being applied to maize and providing the first genome-wide comprehensive view of structural variation and will provide the basis for investigating the interplay between repeats and genes as well as the amount of species level diversity within maize.