Identification, Transcriptome, and Proteome Analysis of Expansin-like Subfamilies in the Storage Root Across I. trifida (2x), Wild (4x, 6x) and Cultivated Sweet Potatoes

The expansin-like subfamilies (EXLA and EXLB) are vital for plant cell wall dynamics, but it remains uncharacterized in wild tetraploid and hexaploid <i>Ipomoea batatas</i>, and its role in the storage root (SR) development is poorly understood. In this work, we identified 4, 3, 3, and 3 EXLAs, alongside 11, 9, 13, and 8 EXLBs, in diploid <i>I. trifida</i> strain Y22, wild tetraploid <i>I. batatas</i> strain Y428B, and hexaploid <i>I. batatas</i> strain Y601, and cultivated sweet potato 'Nancy Hall', respectively. A comprehensive bioinformatic analysis of the expansin-like genes and proteins was performed to reveal their potential roles in SR development. Gene expression profiling showed that <i>EXLA</i> members were expressed during SR development, while approximately half of the <i>EXLB</i> members were expressed in Y22, Y428B (pencil root), Y601, and NH, respectively. Proteomic analysis (4D-DIA) detected 2, 1, 1, and 1 EXLAs, and 3, 3, 3, and 3 EXLBs in the mature SRs of the respective species. Integrated transcriptomic and proteomic analyses suggested that downregulating <i>Iba6xEXLB2</i> and <i>Iba6xEXLB1</i> may be associated with SR swelling in sweet potato. Furthermore, subcellular localization assays confirmed that Iba6xEXLB2 and Iba6xEXLB8 are localized to the cell wall/membrane. This study enhances the understanding of the expansin-like gene subfamily in sweet potato and its wild relatives and lays the groundwork for future functional studies on the role of expansin-like genes in SR development.