Abstract
Pectin methylesterase inhibitor (PMEI) inhibits pectin methylesterase (PME) activity at post-translation level, which plays core roles in vegetative and reproductive processes and various stress responses of plants. However, the roles of PMEIs in tea plant are still undiscovered. Herein, a total of 51 CsPMEIs genes were identified from tea plant genome. CsPMEI1-4 transcripts were varied in different tea plant tissues and regulated by various treatments, including biotic and abiotic stresses, sugar treatments, cold acclimation and bud dormancy. Overexpression of CsPMEI4 slightly decreased cold tolerance of transgenic Arabidopsis associated with lower electrolyte leakage, soluble sugars contents and transcripts of many cold-induced genes as compared to wild type plants. Under long-day and short-day conditions, CsPMEI2/4 promoted early flowering phenotypes in transgenic Arabidopsis along with higher expression levels of many flowering-related genes. Moreover, overexpression of CsPMEI2/4 decreased PME activity, but increased sugars contents (sucrose, glucose, and fructose) in transgenic Arabidopsis as compared with wild type plants under short-day condition. These results indicate that CsPMEIs are widely involved in tea plant vegetative and reproductive processes, and also in various stress responses. Moreover, CsPMEI4 negatively regulated cold response, meanwhile, CsPMEI2/4 promoted early flowering of transgenic Arabidopsis via the autonomous pathway. Collectively, these results open new perspectives on the roles of PMEIs in tea plant.
Highlights
Pectin is one of three major polysaccharides in plant primary cell walls, which plays vital roles in different plant tissues and developmental stages, and in responses to biotic and abiotic stresses
The mRNA levels of FLOWERING LOCUS C (FLC) and an ABA stimulated positive factors, ABSCISIC ACID-INSENSITIVE 5 (ABI5) were decreased both in CsPMEI2OE lines and CsPMEI4-OE lines (Figures 8D, 9D). These results suggested that CsPMEI2 and CsPMEI4 promoting early flowering may partially depend on ABA-dependent pathway. This inference was supported by ABA treatments, where we found the flowering times of CsPMEI2-OE and CsPMEI4-OE lines were delayed by the application of exogenous ABA, even though the development of all plants retarded by ABA treatment (Supplementary Figure 3)
As a type of small molecular protein, Pectin methylesterase inhibitor (PMEI) is encoded by large multigene family in various plant species, such as Arabidopsis (Müller et al, 2013), B. campestris (Liu et al, 2018b), rice (Nguyen et al, 2016), pear (Zhu et al, 2021), etc
Summary
Pectin is one of three major polysaccharides in plant primary cell walls, which plays vital roles in different plant tissues and developmental stages, and in responses to biotic and abiotic stresses. The first PMEI protein (AcPMEI) was identified and purified from kiwi fruit, which has been verified to effectively repress PME activity through formation of a 1:1 non-covalent complex (Balestrieri, 1990; Di Matteo et al, 2005). The four C residues are mainly involved in the formation of two disulfide bridges (S–S), which is critical for the stabilization of four-helical bundle structure (Wormit and Usadel, 2018). These structural properties are found in a type of invertase inhibitor (INH) that shared a structural superimposition with PMEI though their sequence identity is only 20–30%. 78 AtPMEIs in Arabidopsis (Müller et al, 2013), 83 LuPMEIs in flax (Pinzon-Latorre and Deyholos, 2014), 49 OsPMEIs in rice (Nguyen et al, 2016), 95 BoPMEIs in Brassica oleracea (Liu et al, 2018a), 100 BcPMEIs in Brassica campestris (Liu et al, 2018b), 55 SbPMEIs in Sorghum bicolor (Ren et al, 2019), and 42 PbrPMEIs in Pyrus bretschneideri (Zhu et al, 2021) etc. have been identified and characterized in succession
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