An apple sucrose transporter MdSUT2.2 is a phosphorylation target for protein kinase MdCIPK22 in response to drought

Abstract

Sugars increase with drought stress in plants and accumulate in the vacuole. However, the exact molecular mechanism underlying this process is not clear yet. In this study, protein interaction and phosphorylation experiments were conducted for sucrose transporter and CIPK kinase in apple. The specific phosphorylation site of sucrose transporter was identified with mass spectrometry. Transgenic analyses were performed to characterize their biological function. It was found that overexpression of sucrose transporter gene MdSUT2.2 in apple plants promoted sugar accumulation and drought tolerance. MdSUT2.2 protein was phosphorylated at Ser site in response to drought. A DUALmembrane system using MdSUT2.2 as bait through an apple cDNA library got a protein kinase MdCIPK22. Bimolecular fluorescence complementary (BiFC), pull-down and co-immunoprecipitation (Co-IP) assays further demonstrated that MdCIPK22 interacted with MdSUT2.2. A series of transgenic analysis showed that MdCIPK22 was required for the drought-induced phosphylation at Ser site of MdSUT2.2 protein, and that it enhanced the stability and transport activity of MdSUT2.2 protein. Finally, it was found that MdCIPK22 overexpression promoted sugar accumulation and improved drought tolerance in an MdSUT2.2-dependent manner in transgenic apple plants. MdCIPK22-MdSUT2.2 regulatory module shed light on the molecular mechanism by which plant accumulates sugars and enhances tolerance in response to drought stress.

Carbon export from leaves is controlled via ubiquitination and phosphorylation of sucrose transporter SUC2

“…Kinase activity influences the abundance of BvSUT1, either through phosphorylation of the transporter itself or of regulatory proteins (16). For SUCs that are not involved in phloem loading, such as apple MdSUT2.2, regulation via phosphorylation has been shown (15,(17)(18)(19)(20)(21).…”

The Tolerance of Salinity in Rice Requires the Presence of a Functional Copy of FLN2

“…The differences between KO line and WT plants with respect to their ability to fix carbon ( Figure 3C) and synthesize, export, partition, and utilize sucrose ( Figures 3E and 4, Figures 5-7) were more pronounced in plants subjected to salinity stress than in nonstressed plants, while the KO line plants appeared to be particularly sensitive to the stress ( Figures 3A and 8A). Sucrose (and other sugars) are used by stressed plants as an osmoticum [16,19]: for example, plants of the halophytic species Thellungiella halophila respond to high levels of salinity by accumulating a significant concentration of sucrose [32]. The build-up of sugar prompted by salinity (as well as by some other abiotic stressors) is driven by the up-regulation of genes encoding components of sugar synthesis and transport [33].…”

“…Meanwhile Jia et al [36] have shown that AtSUC9 mediates sucrose distribution in a way which supports the plant's tolerance of abiotic stress resistance. Suppression of the aspen (P. tremula) gene PtaSUT4 alters the plant's responsiveness to moisture stress [15], while the over-expression in apple (Malus × domestica) of MdSUT2.2 promotes tolerance to both salinity and drought [16,19]. In rice, both SUT1 and SUT2 contribute to the salinity and drought response [37,38].…”

“…Members of the SUT1 and SUT3 clades are responsible for phloem loading or for sucrose downloading into sink organs [12], while SUT2 members function not only as sucrose transporters but also as low-affinity sugar sensors [13]. Some members of the SUT4 clade, for example, A. thaliana AtSUT4, barley HvSUT2, rice SUT2, bread wheat TaSUT2, Lotus japonicus LjSUT4, and poplar (Populus tremula) PtaSUT4, localize to the vacuolar membrane and function as sucrose/H + symporters [14][15][16]. According to Schulze et al [13] and Reinders et al [9], it is possible that HvSUT2, LjSUC4, and AtSUC4 are also responsible for the release of sucrose from the vacuole.…”

“…According to Schulze et al [13] and Reinders et al [9], it is possible that HvSUT2, LjSUC4, and AtSUC4 are also responsible for the release of sucrose from the vacuole. In various plant species, SUT genes can be induced by a range of abiotic stress factors [17], while transgenic plants constitutively expressing SUT genes not only exhibit an enhanced accumulation of sucrose and soluble sugars, but are also more tolerant of abiotic stress [16,18,19]. Among the monosaccharide transporters, AtTMT1, AtTMT2, and AtTMT3 all contribute to vacuolar glucose import, with AtTMT1 playing a major role during the plants' stress response [20].…”