The vacuolar proton-pumping pyrophosphatase gene (VPP) is often used to enhance plant drought tolerance via genetic engineering.  In this study, the drought tolerance of four transgenic inbred maize lines overexpressing ZmVPP1 (PH4CV-T, PH6WC-T, Chang7-2-T, and Zheng58-T) and their transgenic hybrids was evaluated at various stages.  Under normal and drought conditions, the height and fresh weight were greater for the four transgenic inbred maize lines than for the wild-type (WT) controls at the germination and seedling stages.  Additionally, the transgenic plants exhibited enhanced photosynthetic efficiency at the seedling stage.  In irrigated and non-irrigated fields, the four transgenic lines grew normally, but with increased ear weight and yield compared with the WT plants.  Moreover, the ear weight and yield of the transgenic hybrids resulting from the PH4CV-T×PH6WC-W and Chang7-2-T×Zheng58-W crosses increased in the non-irrigated field.  Our results demonstrated that the growth and drought tolerance of four transgenic inbred maize lines with improved photosynthesis were enhanced by the overexpression of ZmVPP1.  Moreover, the Chang7-2 and PH4CV transgenic lines may be useful for future genetic improvements of maize hybrids to increase drought tolerance.

Drought is one of the most important abiotic stresses affecting maize growth and development and therefore resulting in yield loss.  Thus it is essential to understand molecular mechanisms of drought stress responses in maize for drought tolerance improvement.  The root plays a critical role in plants sensing water deficit.  In the present study, two maize inbred lines, H082183, a drought-tolerant line, and Lv28, a drought-sensitive line, were grown in the field and treated with different water conditions (moderate drought, severe drought, and well-watered conditions) during vegetative stage.  The transcriptomes of their roots were investigated by RNA sequencing.  There were 1 428 and 512 drought-responsive genes (DRGs) in Lv28, 688 and 3 363 DRGs in H082183 under moderate drought and severe drought, respectively.  A total of 31 Gene Ontology (GO) terms were significantly over-represented in the two lines, 13 of which were enriched only in the DRGs of H082183.  Based on results of Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis, “plant hormone signal transduction” and “starch and sucrose metabolism” were enriched in both of the two lines, while “phenylpropanoid biosynthesis” was only enriched in H082183.  Further analysis revealed the different expression patterns of genes related to abscisic acid (ABA) signal pathway, trehalose biosynthesis, reactive oxygen scavenging, and transcription factors might contribute to drought tolerance in maize.  Our results contribute to illustrating drought-responsive molecular mechanisms and providing gene resources for maize drought improvement.

Drought stress affects the growth and productivity of crop plants including sorghum.  To study the molecular basis of drought tolerance in sorghum, we conducted the transcriptomic profiling of sorghum leaves and roots under drought stress using RNA-Seq method.  A total of 510, 559, and 3 687 differentially expressed genes (DEGs) in leaves, 3 368, 5 093, and 4 635 DEGs in roots responding to mild drought, severe drought, and re-watering treatments were identified, respectively.  Among them, 190 common DEGs in leaves and 1 644 common DEGs in roots were responsive to mild drought, severe drought, and re-watering environment.  Gene Ontology (GO) enrichment analysis revealed that the GO categories related to drought tolerance include terms related to response to stimulus especially response to water deprivation, abscisic acid stimulus, and reactive oxygen species.  The major transcription factor genes responsive to drought stress include heat stress transcription factor (HSF), ethylene-responsive transcription factor (ERF), Petunia NAM, Arabidopsis ATAF1/2 and CUC2 (NAC), WRKY transcription factor (WRKY), homeodomain leucine zipper transcription factor (HD-ZIP), basic helix-loop-helix transcription factor (bHLH),  and V-myb myeloblastosis viral oncogene homolog transcription facotr (MYB).  Functional protein genes for heat shock protein (HSPs), late-embryogenesis-abundant protein (LEAs), chaperones, aquaporins, and expansins might play important roles in sorghum drought tolerance.  Moreover, the genomic regions enriched with HSP, expansin, and aquaporin genes responsive to drought stress could be used as powerful targets for improvement of drought tolerance in sorghum and other cereals.  Overall, our results provide a genome-wide analysis of DEGs in sorghum leaves and roots under mild drought, severe drought, and re-watering environments.  This study contributes to a better understanding of the molecular basis of drought tolerance of sorghum and can be useful for crop improvement.