Drought stress inhibits stomatal development to improve water use efficiency in cotton

Stomata play a principal role in adjusting carbon dioxide (CO2) intake and water use for plant adaptation and tolerance to water-restricted conditions. In the present study, impact of water stress-mediated stomatal development in drought-tolerant LRA-5166 and sensitive NBRI-67 cotton varieties was elucidated through transcript level of stomatal genes, leaf gas exchange, stomatal traits, and growth parameters under water stress conditions. Our findings showed that the tolerance of LRA-5166 was associated with higher stomatal density, stomatal index and smaller guard cells as compared to the sensitive NBRI-67. These developmental changes in stomata result in comparatively better stomatal regulation in LRA-5166 than NBRI-67 to transpiration and stomatal conductance. The expression analysis of stomatal genes showed transcript levels of EPIDERMAL PATTERNING FACTOR 2 (EPF2), STOMATAL DENSITY AND DISTRIBUTION 1 (SDD1), and TOO MANY MOUTH (TMM) were distinctly enhanced in both LRA-5166 and NBRI-67 under the water stress, while the transcript level of STOMAGEN (STG) was reduced in both the varieties. The up-regulation of EPF2, SDD1, and TMM genes in sensitive variety reduced the stomatal density and index more than the tolerant variety. Our studies reveal that regulated increase of EPF2, SDD1 and TMM to drought could be involved in plasticity of stomatal numbers and guard cell length and, therefore, more efficiently regulates instantaneous water use efficiency (WUEinst) and plant's ability to combat drought.