Genome-wide analysis of the SWEET gene family in quinoa and functional study of CqSWEET14 in drought resistance.

The SWEET gene family plays important roles in various physiological processes, including sugar transport and regulation, plant development, and environmental adaptation. This study conducted a genome-wide identification, expression analysis, and functional investigation of the SWEET gene family in quinoa. The results revealed a total of 29 CqSWEET genes identified in quinoa, with most CqSWEET proteins being alkaline hydrophobic proteins. Gene structure analysis showed that the number of exons ranged from 1 to 9. The conserved motifs Motif1-7 were highly conserved among family members. Analysis of promoter cis-acting elements revealed that multiple genes contain elements related to hormone responses (ABA, JA) and abiotic stress responses (e.g., drought, low temperature). Chromosomal localization mapping indicated a non-uniform distribution of the genes, and collinearity analysis identified seven pairs of duplicated genes, with their evolution predominantly driven by purifying selection. qRT-PCR analysis showed that under drought stress, CqSWEET genes exhibited diverse expression patterns in leaf and root tissues. Among them, ten genes, including CqSWEET04, 05, 12-14, 19-21, and 27-29, were significantly upregulated in leaves, while genes such as CqSWEET14 and 21 also showed strong responses to drought in roots. Further functional validation demonstrated that overexpression of the CqSWEET14 gene in Arabidopsis significantly enhanced the plants' drought resistance: under mannitol-simulated drought conditions, the root length of transgenic plants increased significantly; under prolonged drought stress, their photosynthetic efficiency (Fv/Fm, Pn, Gs, Tr) and chlorophyll content were significantly higher than those of wild-type plants, while the intercellular CO₂ concentration (Ci) was lower. Additionally, the activities of antioxidant enzymes (SOD, POD, CAT) in transgenic plants were significantly elevated, and malondialdehyde (MDA) content was significantly reduced, indicating enhanced reactive oxygen species scavenging capacity to mitigate oxidative damage. In summary, this study systematically elucidated the fundamental characteristics of the CqSWEET gene family in quinoa, revealed its potential role in drought stress responses, and validated the function of the CqSWEET14 gene in improving plant drought resistance, providing important candidate genes and theoretical foundations for the genetic improvement of stress tolerance in quinoa.