A research team has mapped a family of plant gene regulators across cultivated sweetpotato and three wild relatives, identifying expression patterns associated with the formation of swollen storage roots or slender "pencil roots." By combining genome analysis, RNA sequencing, and protein profiling, the researchers highlighted candidate NAC transcription factors and potential hormone signals involved in root development. The findings provide a foundation for investigating how sweetpotato builds its harvestable roots and could eventually support molecular breeding aimed at improving crop yield.
Sweetpotato yield depends on the formation and enlargement of storage roots, a developmental process involving cell division, cell expansion, and changes to cell walls. Previous research has identified genes involved in wall remodeling and starch accumulation, while studies in other crops have established NAC transcription factors as important regulators of growth and stress responses. However, how this gene family contributes to sweetpotato root enlargement remains poorly understood. The crop's complex hexaploid genome further complicates investigation, and wild relatives differ substantially in their capacity to produce swollen roots. Comparing these contrasting plants offers an opportunity to identify regulatory patterns associated with successful storage root development.
A study (DOI: 10.48130/ph-0026-0022 ) published in Plant Hormones on 29 September 2026 by Ming Li's & Wei Jian's team, Chongqing Normal University, identifies conserved NAC gene families alongside contrasting expression patterns and hormone-responsive promoter elements that suggest candidate mechanisms underlying differences in root swelling.
The researchers compared diploid Ipomoea trifida Y22, wild tetraploid I. batatas Y428B, wild hexaploid I. batatas Y601, and the cultivated variety Nancy Hall. They screened genome-derived protein sequences using sequence similarity searches, NAC-domain models, and conserved-domain verification, then analyzed evolutionary relationships, protein motifs, chromosome locations, and corresponding genomic regions. This workflow identified 134, 142, 132, and 126 NAC genes, respectively: 534 genes in total, grouped into 19 subfamilies and distributed unevenly across 15 chromosomes in each genome. Comparative analysis revealed 292 collinear gene pairs, demonstrating extensive conservation across the four materials. To examine developmental activity, the team collected roots at four stages, from adventitious roots to mature storage roots, with three biological replicates per sampling point. Y428B, which produces pencil roots rather than swollen storage roots, was sampled at matching time points. RNA sequencing revealed that many NAC genes in the three storage-root-forming materials increased their expression as roots developed. In Y428B, most instead showed high early expression followed by a sharp decline, with few displaying sustained increases. The team then used four-dimensional data-independent acquisition proteomics to examine mature-stage roots, detecting 15 NAC proteins across the materials, with three to five detected in each. This limited detection contrasted with the broader transcript profiles, indicating that RNA abundance alone does not fully describe NAC protein accumulation. Iba4xNAC028 was especially abundant in Y428B, while the related proteins Ibw6xNAC022 and Itr2xNAC069 were prominent in wild materials with weaker swelling than Nancy Hall. These associations identify candidates for testing, rather than establish their functions. Finally, analysis of 2,000-base-pair promoter regions for the 15 protein-detected genes found widespread hormone-responsive elements. Sites associated with abscisic acid and methyl jasmonate were most prevalent, while gibberellin-responsive elements were also common, suggesting possible connections between hormone signaling, developmental regulation, and stress responses during root enlargement that merit further experimental investigation.
Together, the findings provide a comparative resource for exploring sweetpotato storage root development. They suggest that differences in when NAC genes become active, which proteins accumulate, and how genes respond to hormonal signals may help explain contrasting root forms. Future hormone-treatment experiments and genetic validation will be needed to determine whether these candidates can be used to improve storage root growth and yield.
