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.