**5. Molecular responses of sugarcane under drought**

During drought stress, the molecular responses include regulation of various signaling molecules, transcription factors (TFs) and drought induced genes (DIGs), which interact with each other and confer the drought tolerance potential to individual genotypes. Some of the major genes involved in drought tolerance are presented in **Table 1**. The genes are classified into two major categories: genes encoding functional proteins, and genes encoding regulatory proteins. Functional proteins play an important role in the protection of cells against dehydration, including late embryogenesis abundant (LEA) proteins, aquaporins (AQP), heat shock proteins (HSPs), ion transporters and metabolic enzymes. Regulatory proteins comprise calcium-binding proteins, protein kinases, transcription factors and signaling factors which can cause changes in plant physiology through signal transduction pathways, and regulate the expression of downstream genes [96]. LEA proteins exhibit important dehydrating protective functions during the late stage of embryo development in seeds. They play a key role in dehydration tolerance by capturing enough water into the cell. LEA proteins are composed of a high proportion of polar amino acids which makes them hydrophilic in nature, and can scavenge reactive oxygen species [96]. Transcription factors are one of the master regulators under stress, causing a significant change in gene expression. Manipulation of these regulatory elements may be beneficial for the enhancement of drought tolerance in sugarcane. It is now well established that both the transcription activators and repressors are involved in the drought stress tolerance [97, 98]. The major TF families involved in drought stress responses are WRKY, MYB, bZIP, NAC and DREB, which are perfect choices for genetic engineering to enhance stress tolerance. The most extensively studied TF family is WRKY which helps in regulating different physiological and metabolic processes [99]. The WRKY TF binds to the conserved DNA cis-element W-box to regulate further downstream processing of plant defense. Liu et al. [90] isolated and characterized the expression of WRKY TF of sugarcane using *E. coli* vector. It was observed that with the increase in the duration of stress, the relative expression level of WRKY increased, hence conferring drought tolerance in sugarcane.

To better understand the molecular basis of the physiological responses of sugarcane under stress conditions, high throughput gene expression studies have been conducted [48, 100–102]. Drought stress induces extensive signal transduction *Physiological and Molecular Adaptation of Sugarcane under Drought vis-a-vis Root System Traits DOI: http://dx.doi.org/10.5772/intechopen.103795*

