Characterization of drought-inducible promoter of PvHVA1 for drought-tolerant improvement in switchgrass (Panicum virgatum L.)

Drought stress occurs intermittently and severely constrains plant growth and production. Constitutive overexpression of stress-responsive genes can improve drought tolerance but often imposes unnecessary metabolic costs under favorable conditions. Stress-inducible promoters therefore represent an important regulatory resource for precision engineering of drought tolerance. In this study, a drought-inducible promoter from switchgrass (Panicum virgatum L.), PvHVA1pro, derived from the late embryogenesis abundant gene PvHVA1 (Hordeum vulgare aleurone 1) was identified and functionally validated. Transcript analysis showed that PvHVA1 expression is strongly induced by PEG-mediated osmotic stress, with minimal basal expression under non-stress conditions. Stable transgenic switchgrass expressing PvHVA1pro::GUS exhibited drought-dependent and reversible promoter activity in vegetative tissues. To demonstrate its practical utility, PvHVA1pro was used to drive the aquaporin gene PvPIP2;9 in switchgrass that the inducible expression of PvPIP2;9 enhanced drought tolerance, photosynthetic performance, and water-use efficiency compared with wild-type plants, without pronounced growth penalties. Together, these results establish PvHVA1pro as a sensitive, low-basal, drought-inducible promoter resource for switchgrass, providing an enabling regulatory tool for functional genomics and precision drought-tolerance engineering in bioenergy crops.