Salinity affects SLs signaling pathway by regulating the expression of SaD14 and SaD53
Another two genes involved in SLs signal transduction (SaD14 ,SaD53 ) were also amplified and sequenced (Supplementary Table S2, Supplementary Table S3). As a non-canonical hormone receptor, D14was reported to express in all tissues, especially in parenchyma cells surrounding the xylem in leaves, stems and axillary buds (Arite et al. , 2009; Yao et al. , 2016). Our result found that a higher expression of SaD14 were observed in leaves, roots and nodes but lower in stems, buds and rhizomes (Figure 5c). To our knowledge, moreSaD14 expressed in roots and nodes would help plant to perceive the SLs and control the tillering process. Moreover, D53 , which was proposed as a repressor in SLs signaling pathway, was reported to mainly expressed in leaves, shoot bases of seedlings, panicles and buds (Jiang et al. , 2013). We also found the same expression pattern of SaD53 in different tissues of S. alterniflora (Figure 5d). According to these results, the nodes of S. alternifloraseedlings were used to evaluate the expressional levels of SaD14and SaD53 under different salinity treatments.
Our qRT-PCR results showed that the expression level of SaD14 in 15‰ salinity treatment was extremely lower than another two salt treatments. As reported by Yao et al. (2016), the D14defect mutant of Arabidopsis (d14-5 ) exhibited a highly branched and low sensitivity to SLs addition. On the contrary, Zhuanget al. (2017) reported that less tillers were found inFestuca arundinacea seedlings with a rise of FaD14transcriptional level. In other words, less D14 in plant would promote the tillering process. Moreover, OsD53 has previously identified as a repressor in SLs signaling pathway in rice (Jiang et al. , 2013). The d53 defect mutant of rice was insensitive to SLs signaling and leading to a dwarf and more tillering (Jiang et al. , 2013). It was clearly that the accumulation of OsD53 would promote the tillering formation in rice (Jiang et al. , 2013). Our quantitative results showed that the expression level of SaD53was constantly increased with the treatment time under 15‰ salinity but had no change or slightly increased under 0‰ salinity treatment or 30‰ salinity treatment, respectively (Figure 6d). Based on above results and analyses, we concluded that the moderate salinity could facilitate the tillering process by reducing the expression of SaD14 but promoting the expression of SaD53 in S. alterniflora basal nodes.