Understanding the Molecular Mechanisms for Alleviating Boron Deficiency in Indian Mustard

Abstract

Boron (B) is an essential micronutrient required for the optimal growth and development of vascular plants. Globally B deficiency is the second most important micronutrient deficiency that causes significant yield reductions in crop plants. Often, seed yield and quality are compromised in plants grown under limited soil B availability without any apparent visual symptoms. B forms borate diester crosslinking with a pectic polysaccharide, rhamnogalacturonan II, during the cell wall formation and therefore, B deficiency primary affects meristem growth, vitality of the pollen grains, flower development and seed set. Brassica juncea is an important oilseed crop in India and other parts of the world and is extremely sensitive to B deficiency. Although the application of foliar B fertilizer improves the yield significantly in B. juncea, excessive application of B can be toxic due to the narrow window between its deficiency and toxicity. Molecular mechanisms of B transport have been initiated by the discovery of B transporters in Arabidopsis thaliana. Several aquaporins (AQP’s) and borate efflux transporter (BORs) family genes have been reported to be involved in the efficient uptake and translocation of B to maintain optimal plant growth under low soil B condition and B exclusion under high soil B conditions. Soil B content in major mustard producing states of India is potentially low and hence it is important to study the B transport mechanisms in B. juncea for the optimal yield.