Abstract
The deposition and degradation of starch in plants is subject to extensive post-translational regulation. To permit degradation of B-type crystallites present in tuberous and leaf starch these starch types are phosphorylated by glucan, water dikinase (GWD). At the level of post-translational redox regulation, ADPglucose pyrophosphorylase, β-amylase (BAM1), limit dextrinase (LD), the starch phosphorylator GWD and the glucan phosphatase dual-specificity phosphatase 4 (DSP4), also named starch excess 4 (SEX4), are reductively activated in vitro. Redox screens now suggest the presence of a substantially more extensive and coordinated redox regulation involving a larger number of enzymes. Noticeably several of these enzymes contain a new type of low-affinity carbohydrate-binding module that we term a low-affinity starch-binding domain or LA-SBD. These are present in the CBM20, CBM45 and CBM53 families and can enable diurnal dynamics of starch–enzyme recognition. Such diurnal changes in starch binding have been indicated for the redox-regulated GWD and SEX4.
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