Abstract
Stylosanthes (stylo) species are commercially significant tropical and subtropical forage and pasture legumes that are vulnerable to chilling and frost. However, little is known about the molecular mechanisms behind stylos’ responses to low temperature stress. Gretchen-Hagen 3 (GH3) proteins have been extensively investigated in many plant species for their roles in auxin homeostasis and abiotic stress responses, but none have been reported in stylos. SgGH3.1, a cold-responsive gene identified in a whole transcriptome profiling study of fine-stem stylo (S. guianensis var. intermedia) was further investigated for its involvement in cold stress tolerance. SgGH3.1 shared a high percentage of identity with 14 leguminous GH3 proteins, ranging from 79% to 93%. Phylogenetic analysis classified SgGH3.1 into Group Ⅱ of GH3 family, which have been proven to involve with auxins conjugation. Expression profiling revealed that SgGH3.1 responded rapidly to cold stress in stylo leaves. Overexpression of SgGH3.1 in Arabidopsis thaliana altered sensitivity to exogenous IAA, up-regulated transcription of AtCBF1-3 genes, activated physiological responses against cold stress, and enhanced chilling and cold tolerances. This is the first report of a GH3 gene in stylos, which not only validated its function in IAA homeostasis and cold responses, but also gave insight into breeding of cold-tolerant stylos.
Highlights
Species of Stylosanthes are among the most economically important forage and pasture legumes in tropical and subtropical regions of Asia, Africa, South America, and Australia [1]
The results indicated that SgGH3.1 responded to low temperature rapidly in stylo leaves and SgGH3.1 overexpression changed IAA sensitivity, increased transcription of AtCBF1-3 genes, triggered physiological responses to cold stress, and improved chilling and cold tolerance in Arabidopsis
Gretchen-Hagen 3 (GH3).1 proteins indicates that SgGH3.1 belongs to Group II of GH3 family (Figure 1A)
Summary
Species of Stylosanthes (stylo) are among the most economically important forage and pasture legumes in tropical and subtropical regions of Asia, Africa, South America, and Australia [1]. S. guianensis exhibits high tolerance to drought and soil infertility, but are very vulnerable to frost and chilling stress [3,4], which makes it difficult for most stylo cultivars to survive through winter even in subtropical areas such as Guangzhou (113◦ 210 5000 , 23◦ 100 1000 ). Intermedia) is a variety of S. guianensis, but it is morphologically and physiologically very different from the other varieties of this species. It is a much smaller plant with maximum height of 30–40 cm and stem diameter < 3 mm, compared with common stylos which usually have a maximum height over 100 cm and old stems highly coarse and woody. Understanding molecular mechanisms associated with cold responses and tolerance in fine-stem stylo could aid in the development of cold-tolerant cultivars capable of surviving subtropical winters
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