Sugarcane Transcription Factor ScbZIP21 has Negative Impact on Biomass Accumulation in Rice Transgenic Plants Under Drought Conditions

Transcription factors are major players in water stress signaling. In recent years, different bZIP transcription factors have been characterized for their involvement in drought response. From a previous experiment conduced with two sugarcane cultivars contrasting to drought tolerance, the transcription factor ScbZIP21 was identified as differentially expressed under drought stress. Functional analysis of ScbZIP21 was conduced in rice as a monocot model plant. The full-length sequence of ScbZIP21 was successfully isolated from sugarcane cultivar ‘IACSP94-2094’, and overexpression vector was obtained by gateway multi-recombination carrying the ubiquitin promoter and hygromycin phosphotransferase (hptII) gene as selectable marker. The relative expression of transgene was evaluated by the 2^-ΔCt method, and T-DNA copy number was obtained by Taqman® assay using hptII gene. Two different transgenic lines nominated of 8 and 9 with a single copy T-DNA insertion, were cultivated at greenhouse and subjected to water restriction. Total dry weight (TDW), relative water content (RWC) and water potential (Y) were measured at the beginning of water deficit (one day after withholding) and at the maximum water deficit (10 days of water withholding), when plants presented significant leaf wilting. The 8 and 9 transgenic lines showed no difference for RWC and Y. However, transgenic lines 7 and 8 showed a reduction of 55,1% and 54,5% in biomass content TDW relative to wild type in drought treatment and well-watered treatment respectively. Therefore, based on these results, the overexpression of ScbZIP21 in transgenic lines showed not be involved with drought tolerance in rice, but involved with negative impacts on biomass accumulation.