Cluster bean: From garnering industrial importance to molecular research interventions for the improvement of commercially viable traits

Abstract

Cluster bean commonly known as guar is a drought-tolerant sub-tropical legume. A large portion of the guar seed endosperm is constituted by galactomannan, which deposits as a thickening of the endosperm cell wall during seed development. Guar galactomannan, commonly called guar gum, is widely used in various industries as a thickening, binding and stabilizing agent. We present a comprehensive review of the molecular underpinnings of the biological phenomena involved in galactomannan biosynthesis in guar. We discuss the advances made in guar genetic engineering for agronomic trait improvement. The progress made in next generation sequencing for deciphering the transcriptomic landscape of galactomannan biosynthesis, stress tolerance and molecular marker identification in guar is being reviewed. A critical analysis of the identified guar small RNAs is presented and their possible involvement in regulating galactomannan biosynthesis is discussed. We have attempted detailed illustration of plant tissue culture and in vitro regeneration in guar and discussed the future scope of utilization of these protocols for guar improvement. This review insightfully analyzes how further application of advanced molecular techniques could be helpful in further improvement of commercially viable traits in guar.