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

Zexun Huai,Lishun Peng,Sheliang Wang,Fangsen Xu,Hua Zhao,Lei Shi

doi:10.3389/fpls.2018.00736

Abstract

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.

Highlights

Boron (B) is essential for the development and growth of higher plants (Warington, 1923)
B plays an important structural role in the crosslinking of cell wall rhamnogalacturonan II (RG-II) to form a stable three-dimensional pectic network which contributes to the mechanical properties of cell wall structure (Funakawa and Miwa, 2015), or vice versa, and many of the effects associated with B deficiency could be the consequence of a disturbed cell wall structure (Camacho-Cristóbal et al, 2015)
To elucidate whether the low-B tolerance of lbt mutant is mediated by B transportrelated genes, we investigated the expression of NIP5;1, NIP6;1, NIP7;1, BOR1, BOR2, BOR3, and BOR4 in lbt mutant by RTqPCR

Summary

Introduction

Boron (B) is essential for the development and growth of higher plants (Warington, 1923). B deficiency hampers many physiological and Tolerance of lbt to B Limitation metabolic aspects of plants, including sugar transport, cell wall structure, photosynthesis, starch granule synthesis and the metabolism of indole acetic acid (Herrera-Rodríguez et al, 2010; Li et al, 2015). In Arabidopsis thaliana, genes involved in B uptake and transport have been cloned, and they include the BOR transporter gene family and NIP (NOD26-like intrinsic proteins) channel gene family. BOR2 is essential for effective RG-II cross linking in the cell wall and root elongation under B limitation (Miwa et al, 2013).

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