Silencing GhFAR3.1 reduces wax accumulation in cotton leaves and leads to increased susceptibility to drought stress.

Fatty acyl-CoA reductases (FAR) are involved in plant wax synthesis and play important roles in plant growth and development. However, little information is available for cotton FAR genes. In this study, we carried out a genome-wide identification of FAR genes in Upland cotton (Gossypium hirsutum L.) and found 10 GhFARs that form five pairs of homoeologs (GhFAR2A to GhFAR3.4D) distributed on six chromosomes. The 10 GhFARs were separated into two subfamilies. Most GhFARs showed tissue-specific expression patterns, and at least one GhFAR of each pair of homoeologs was relatively highly expressed in at least one of the tissues investigated. GhFAR3.1 was highly expressed in leaves. The function of GhFAR3.1 in wax accumulation and drought tolerance was analyzed using virus-induced gene silencing (VIGS). Silencing GhFAR3.1 reduced the total wax content and relative water content of leaves by over 60% and 13%, respectively, suggesting a role of GhFAR3.1 in wax synthesis and protection against water loss. Compared to the well-watered conditions, drought stress induced significant accumulation of wax in leaves of wild-type plants but not in leaves of GhFAR3.1 silenced plants, leading to less water holding capacity in GhFAR3.1 silenced plants and plant wilting. Silencing GhFAR3.1 had no effect on the expression levels of the wax biosynthesis pathway genes KAS, KCS, and LACS (upstream GhFAR3.1), but reduced the transcript level of its downstream gene WSD. Together, these results suggest that leaf wax content is important for water retention and drought tolerance and that GhFAR3.1 is essential for wax synthesis in cotton leaves. These results also provide the basis for further study on the molecular regulation mechanism of GhFARs in cotton development and surface lipid synthesis.