Systematic Analysis of Stay-Green Genes in Six Ipomoea Species Reveals the Evolutionary Dynamics, Carotenoid and Anthocyanin Accumulation, and Stress Responses of Sweet Potato.

Abstract

Background/objectives: Stay-green proteins (SGRs) play a vital role in regulating plant chlorophyll degradation and senescence. However, this gene family has not been explored in Ipomoea species and sweet potato.

Methods: A total of 19 SGR family genes (SGRs) were identified using Basic Local Alignment Search Tool (BLAST) methods. The proteins' physiological properties, evolutionary and phylogenetic relationships, conserved domain and motifs, gene structures, collinearity, and promoter cis-elements were systematically analyzed. Moreover, expression patterns and protein interaction network analyses were performed for sweet potato.

Results: In this study, we identified 19 SGRs in six Ipomoea species. These SGRs were divided into four subgroups according to their phylogenetic relationships. Domian analysis revealed that SGRs had the conserved "stay-green" domain. Gene structure analysis showed that SGRs had similar structures. The collinearity analysis revealed that the SGRs originated from two genes, with one gene undergoing duplication during evolution history; moreover, the SGRs experienced rearrangement throughout the evolutionary process in the Ipomoea species. Cis-elements related to pigment biosynthesis and hormone and stress responses were found. In addition, expression pattern analysis showed that IbSGRs, especially IbSGR1, IbSGR2, and IbSGR3, might play an important role in pigment accumulation. The SGRs could also respond to stress responses (i.e., cold, drought, and salt) and take part in hormone crosstalk (i.e., abscisic acid (ABA), methyl jasmonate (MeJA), salicylic acid (SA)).

Conclusions: Taken together, the findings of this study provide new insights for further understanding the functions of SGRs and candidate genes for pigment accumulation and stress tolerance in sweet potatoes.