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. 2016 Apr 4;171(2):833–848. doi: 10.1104/pp.16.00173

Figure 12.

Figure 12.

CGR2- and CGR3-mediated pectin methylesterification regulates the relationship between photosynthesis and plant growth. A schematic diagram outlining how (A) suppression or (B) over-expression of CGR2 and CGR3 gene expression affects the relationship between photosynthesis and plant growth in Arabidopsis is presented. Suppression of CGR2 and CGR3 reduces the degree of pectin methylation, which leads to an increase in cell-to-cell adhesion, cation-mediated cross linking of GalUA, and consequent hardening of cell walls. CGR2 over-expression increases the degree of pectin methylation, which allows cell expansion through reduced cell-to-cell adhesion and cation-mediated cross linking. We propose that pectin methyltransferase enzyme, through its ability to directly alter cell expansion, determines the amount of C partitioned to leaf area growth versus growth in terms of LMA. For example, while more C is partitioned to growth in terms of LMA in the CGR2 and CGR3 double knockout mutant, in the CGR2 over-expression line more C is partitioned to leaf area growth. An increase in LMA leads to enhanced area-based respiration and a reduction in leaf area contribute to a reduction in whole plant photosynthesis. Collectively, this results in a reduction in C available for growth and consequently a decrease in overall plant growth; an opposite trend is seen in CGR2OX. Thus, CGR2 and CGR3, through their ability to alter the degree of methylated pectin in the cell wall of the mesophyll cells, determine how photosynthate is utilized to grow the plant. In other words, CGR2- and CGR3-mediated pectin methylesterification affects the relationship between photosynthesis and plant growth by regulating the proportions of C that is partitioned to leaf area growth and LMA. Final overall growth mainly depends on the expression patterns of CGR2 and CGR3 and how much C is partitioned to area growth and LMA and not on area-based photosynthesis. PME: pectin methylesterase; PMEI: PME inhibitor; PMT: pectin methyltransferase. CH3OH is methanol.