Abstract
Sweet potato (Ipomoea batatas [L.] Lam.) is an important subsistence crop in Sub‐Saharan Africa, yet as for many crops, yield can be severely impacted by drought stress. Understanding the genetic mechanisms that control drought tolerance can facilitate the development of drought‐tolerant sweet potato cultivars. Here, we report an expression profiling study using the US‐bred cultivar, Beauregard, and a Ugandan landrace, Tanzania, treated with polyethylene glycol (PEG) to simulate drought and sampled at 24 and 48 hr after stress. At each time‐point, between 4,000 to 6,000 genes in leaf tissue were differentially expressed in each cultivar. Approximately half of these differentially expressed genes were common between the two cultivars and were enriched for Gene Ontology terms associated with drought response. Three hundred orthologs of drought tolerance genes reported in model species were identified in the Ipomoea trifida reference genome, of which 122 were differentially expressed under at least one experimental condition, constituting a list of drought tolerance candidate genes. A subset of genes was differentially regulated between Beauregard and Tanzania, representing genotype‐specific responses to drought stress. The data analyzed and reported here provide a resource for geneticists and breeders toward identifying and utilizing drought tolerance genes in sweet potato.
Highlights
Sweet potato (Ipomoea batatas [L.] Lam.) is grown worldwide for its nutrient‐rich storage roots
Wilted and chlorotic leaves were observed in polyethylene glycol (PEG)‐treated plantlets of both varieties by 24 hr after stress (HAS), and the severity increased at 48 HAS (Figure 1a), with plants dying after 21 days
Overall expression patterns were conserved between Beauregard and Tanzania, and consistent with drought responses reported in the literature, with a general upregulation of abscisic acid (ABA) signaling components and downregulation of tissue growth processes
Summary
Sweet potato (Ipomoea batatas [L.] Lam.) is grown worldwide for its nutrient‐rich storage roots. Tolerance among sweet potato germplasm suggests that drought tolerance loci can be introgressed into drought‐sensitive cultivars. Kivuva et al (2015) in a study involving 84 total genotypes showed that Beauregard differs from Tanzania in several drought response traits. Global gene expression patterns in leaf tissue of two varieties of I. batatas, Beauregard, and Tanzania, during PEG‐simulated drought stress were characterized with RNA‐Sequencing (RNA‐Seq); diploid I. trifida, which is closely related to I. batatas and is a putative progenitor species (Austin, 1988; Kobayashi, 1983), was used as the reference genome sequence (http://sweetpotato.plantbiology.msu.ed u/gt4sp_download.shtml). Expressed genes (DEGs) were identified, revealing candidate genes for improving drought tolerance in sweet potato. Data from this study will be useful in identifying candidate genes within drought tolerance QTL and improving drought tolerance in this key food security crop
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