Strigolactones in Sugarcane Growth and Development

Sugarcane is a complex polyploid aneuploid cash crop, and transgenic varieties are important for molecular genetic and traditional breeding approaches. Herein, the sugarcane variety ROC22 served as the receptor, the <i>Bar</i> gene served as a screening marker, and positive and negative fragments of the <i>ScD27.2</i> gene, upstream of strigolactones (SLs) biosynthesis genes driven by the <i>35S</i> promoter, were introduced by <i>Agrobacterium tumefaciens</i>-mediated transformation. Regenerated plants were obtained by co-culture, screening culture, and differentiation induction, and 27 sense and antisense <i>ScD27.2</i> transgenic seedlings were obtained by herbicide screening. PCR detection and 1% Basta (Glufosinate) application on leaves revealed <i>Bar</i> in all lines, with all testing positive for herbicide application and 23 containing the target gene (positive resistance screening rate = 87.5%). q-PCR and phenotypic analyses showed that <i>ScD27.2</i> expression, plant height, tiller number, root length, stem diameter, and fresh weight were decreased in transgenic (ScD27.2R-9) compared with non-transgenic (NT and ScD27.2F-2) lines. <i>ScD27.2</i> expression was downregulated, and growth potential was inhibited. Under 20% PEG treatment, malondialdehyde (MDA) content in ScD27.2R-9 was higher than in NT, while proline content was lower. Under drought stress, <i>ScD27.2</i> expression, MDA levels, and proline content in ScD27.2F-2 and NT were higher than in non-treated controls, <i>ScD27.2</i> expression increased with time, and MDA and proline levels also increased. <i>ScD27.2</i> expression in ScD27.2R-9 decreased under 20% PEG treatment, MDA and proline increased (but not to NT levels), and growth was lower than NT. The 20% PEG treatment also increased the levels of (±)-2′-epi-5-deoxystrigol and (+)-abscisic acid in the rooting culture media of ScD27.2F-2, ScD27.2R-9, and NT lines, but the levels of (+)-abscisic acid content in ScD27.2R-9 was lower than in NT. Thus, interfering with <i>ScD27.2</i> expression decreased resistance to 20% PEG treatment. <i>ScD27.2</i> encodes a β-carotene isomerase involved in SLs biosynthesis that might function in sugarcane resistance to drought stress. It explains the role of SLs in sugarcane growth and development and responses to drought stress.