Natural variation and genetic analysis of the tiller angle gene MsTAC1 in Miscanthus sinensis.

Biomass yield is an important target trait in Miscanthus breeding for desirable energy crops. Tiller angle is a key trait of plant architecture because it determines planting density and further influences biomass yield through affecting photosynthesis efficiency. TAC1, a major gene involved in tiller and leaf angle control in rice and maize, respectively, has been extensively studied. Nucleotide variation at this gene, MsTAC1, was investigated in 33 Miscanthus sinensis accessions collected from different areas in China, and one genotype of Miscanthus × giganteus. A total of 136 loci, including 129 single base substitutions and seven InDels, occurred within the MsTAC1 gene of 1,874 bp. The genetic diversity at MsTAC1 is characterized by high nucleotide diversity (π value) and high heterozygosity. Clustering analysis indicated that the phylogenetic tree of the 33 M. sinensis accessions was correlated with their geographical sites of origin. The neutrality test revealed no strong selection pressure on coding and non-coding region variations of the MsTAC1 gene in the accessions. Phenotype evaluations were conducted for tiller angle and five other traits in the Miscanthus panels in the first two growth years of 2009 and 2010. Analysis of variance showed significant phenotypic variations in the examined traits. Association analysis using 246 markers detected 88 loci associated with all the test traits in either 1 or 2 years, and 11 of the 88 were year reproducible and thus reliable. These associations indicate that the variation of MsTAC1 affects the phenotypic value of the tiller angle, tiller number and biomass yield, suggesting that allelic variation in MsTAC1 affects multiple traits and demonstrates its significance in Miscanthus breeding programs.

Identification and Characterization of an Arabidopsis thaliana Mutant lbt With High Tolerance to Boron Deficiency.

Boron (B) is an essential micronutrient of plants. In the present study, we characterized an Arabidopsis mutant lbt with significant low-boron tolerance that was identified based on our previous mapping of QTL for B efficiency in Arabidopsis. Multiple nutrient-deficiency analyses point out that lbt mutant is insensitive to only B-limitation stress. Compared with wild-type Col-0, the fresh weight, leaf area, root length and root elongation rate of lbt mutant were significantly improved under B deficiency during vegetative growth. lbt mutant also showed the improvements in plant height, branches and inflorescences compared with Col-0 during the reproductive stage under B limitation. Ultrastructure analysis of the leaves showed that starch accumulation in lbt mutant was significantly diminished compared with Col-0. Furthermore, there were no significant differences in the expression of transporter-related genes and B concentrations between Col-0 and lbt mutant under both normal B and low-B conditions. These results suggest that lbt mutant has a lower B demand than Col-0. Genetic analysis suggests that the low-B tolerant phenotype of lbt mutant is under the control of a monogenic recessive gene. Based on the high-density SNP linkage genetic map, only one QTL for low-B tolerance was mapped on chromosome 4 between 10.4 and 14.8 Mb. No any reported B-relative genes exist in the QTL interval, suggesting that a gene with unknown function controls the tolerance of lbt to B limitation. Taken together, lbt is a low-B tolerant mutant that does not depend on the uptake or transport of B and is controlled by a monogenic recessive gene mapped on chromosome 4, and cloning and functional analysis of LBT gene are expected to reveal novel mechanisms for plant resistance to B deficiency.