Fruit Softening: Revisiting the Role of Pectin

Fruit softening is a major determinant of shelf life and commercial value. Here, we highlight recent work that revisits the role of pectin in fruit softening and primary cell wall structure. These studies demonstrate the importance of pectin and the link between its degradation and softening in fleshy fruits. Fruit softening, which is a major determinant of shelf life and commercial value, is the consequence of multiple cellular processes, including extensive remodeling of cell wall structure. Recently, it has been shown that pectate lyase (PL), an enzyme that degrades de-esterified pectin in the primary wall, is a major contributing factor to tomato fruit softening. Studies of pectin structure, distribution, and dynamics have indicated that pectins are more tightly integrated with cellulose microfibrils than previously thought and have novel structural features, including branches of the main polymer backbone. Moreover, recent studies of the significance of pectinases, such as PL and polygalacturonase, are consistent with a causal relationship between pectin degradation and a major effect on fruit softening. Fruit softening, which is a major determinant of shelf life and commercial value, is the consequence of multiple cellular processes, including extensive remodeling of cell wall structure. Recently, it has been shown that pectate lyase (PL), an enzyme that degrades de-esterified pectin in the primary wall, is a major contributing factor to tomato fruit softening. Studies of pectin structure, distribution, and dynamics have indicated that pectins are more tightly integrated with cellulose microfibrils than previously thought and have novel structural features, including branches of the main polymer backbone. Moreover, recent studies of the significance of pectinases, such as PL and polygalacturonase, are consistent with a causal relationship between pectin degradation and a major effect on fruit softening. a scanning probe microscope where the microscope probe interacts with the sample and allows imaging and measuring of samples at nanoscales. Deflection of the probe by the sample is converted into an electrical signal. highly complex extracellular matrix outside the plasma membrane of plant cells comprising a range of polysaccharides and proteins. The main functions of the cell wall include generating turgor pressure, controlling cell expansion, cell adhesion, support, and protection against mechanical stress. an enzyme that hydrolyzes the β-1,4 glycosidic bonds between galactose residues in pectin β (1-4) galactans that form side-chains on RG-I. a layer between the cell walls of two adjacent plant cells that is rich in pectin. an enzyme that causes eliminative cleavage of polymers of α-1,4 galactosyluronic acid molecules to give oligosaccharides with 4-deoxy-α-D-galact-4-enuronosyl groups at their nonreducing ends. PL preferentially acts on HG from which methyl esters have first been removed by PME. also known as pectic polysaccharides, a group of structurally complex molecules with a backbone of α-1,4 galactosyluronic acid residues and that may also have other sugar residues present as side-chains or in the backbone itself. These can include rhamnose, galactose, and arabinose. Three main classes of pectin are recognized: (i) HG, which comprises a backbone of 1,4-linked α-D-galacturonosyluronic acid residues; (ii) RG-I, comprising interspersed α-D-galacturonosyl residues and rhamnosyl residues, with side-chains of galactosyl and arabinosyl residues; and (iii) RG-II, which is less abundant than the other two classes, but has a complex composition. an enzyme that catalyzes the removal of the methyl ester groups from pectin. an enzyme that can hydrolyze the α-1,4 glycosidic bonds in galactosyluronic acid polymers and, therefore, can hydrolyze HG. a polymer of uronic acid residues; in plant cell walls, these would comprise a backbone of α-1,4 galactosyluronic acid residues with or without other sugar residues being present. Therefore, polyuronides are synonymous with pectin in this context and can refer to any pectic polymers with a high proportion of galactosyluronic acid residues, including HG and RG-I. a process whereby RNA molecules can be used to target and silence the expression of a specific gene of interest. a spectroscopic technique for studying the atomic structure of materials in the solid state by manipulating and correlating spin states of nuclei using strong magnetic fields. a cell wall polysaccharide with a backbone of β1-4-linked glucose residues, most of which are substituted with 1-6 linked xylose side-chains.