Overexpression of two DELLA subfamily genes MiSLR1 and MiSLR2 from mango promotes early flowering and enhances abiotic stress tolerance in Arabidopsis.

Gibberellic acids (GAs) are a group of endogenous phytohormones that play important roles in plant growth and development. SLENDER RICE (SLR) serves as a vital component of the DELLA gene family, which plays an irreplaceable role in regulating plant flowering and height, as well as stress responses. SLR gene has not been reported in mango, and its function is unknown. In present study, two DELLA subfamily genes MiSLR1 and MiSLR2 were identified from mango. MiSLR1 and MiSLR2 were highly expressed in the stems of the juvenile stage, but were expressed at a low level in flower buds and flowers. Gibberellin treatment could up-regulate the expression of MiSLR1 and MiSLR2 genes, but gibberellin biosynthesis inhibitor prohexadione-calcium (Pro-Ca) and paclobutrazol (PAC) treatments significantly down-regulated the expression of MiSLR1, while MiSLR2 was up-regulated. The expression levels of MiSLR1 and MiSLR2 were up-regulated under both salt and drought treatments. Overexpression of MiSLR1 and MiSLR2 genes significantly resulted early flowering in transgenic Arabidopsis and significantly up-regulated the expression levels of endogenous flower-related genes, such as SUPPRESSOR OF CONSTANS1 (SOC1), APETALA1 (AP1), and FRUITFULL (FUL). Interestingly, MiSLR1 significantly reduced the height of transgenic plants, while MiSLR2 gene increased. Overexpression of MiSLR1 and MiSLR2 increased seed germination rate, root length and survival rate of transgenic plants under salt and drought stress. Physiological and biochemical detection showed that the contents of proline (Pro) and superoxide dismutase (SOD) were significantly increased, while the contents of malondialdehyde (MDA) and HO were significantly decreased. Additionally, protein interaction analysis revealed that MiSLR1 and MiSLR2 interacted with several flowering-related and GA-related proteins. The interaction between MiSLR with MiGF14 and MiSOC1 proteins was found for the first time. Taken together, the data showed that MiSLR1 and MiSLR2 in transgenic Arabidopsis both regulated the flowering time and plant height, while also acting as positive regulators of abiotic stress responses.