Abstract
Pectin synthesis and modification are vital for plant development, although the underlying mechanisms are still not well understood. Here, we report the functional characterization of the OsTSD2 gene, which encodes a putative methyltransferase in rice. All three independent T-DNA insertion lines of OsTSD2 displayed dwarf phenotypes and serial alterations in different zones of the root. These alterations included abnormal cellular adhesion and schizogenous aerenchyma formation in the meristematic zone, inhibited root elongation in the elongation zone, and higher lateral root density in the mature zone. Immunofluorescence (with LM19) and Ruthenium Red staining of the roots showed that unesterified homogalacturonan (HG) was increased in Ostsd2 mutants. Biochemical analysis of cell wall pectin polysaccharides revealed that both the monosaccharide composition and the uronic acid content were decreased in Ostsd2 mutants. Increased endogenous ABA content and opposite roles performed by ABA and IAA in regulating cellular adhesion in the Ostsd2 mutants suggested that OsTSD2 is required for root development in rice through a pathway involving pectin synthesis/modification. A hypothesis to explain the relationship among OsTSD2, pectin methylesterification, and root development is proposed, based on pectin's function in regional cell extension/division in a zone-dependent manner.
Highlights
Pectin is structurally and functionally the most complex polysaccharide in plant cell walls (Mohnen, 2008)
Increased endogenous abscisic acid (ABA) content and opposite roles performed by ABA and indole-3-acetic acid (IAA) in regulating cellular adhesion in the Ostsd2 mutants suggested that OsTSD2 is required for root development in rice through a pathway involving pectin synthesis/modification
OsTSD2 is predicted to be localized in the Golgi body, which is consistent with its putative role at the site of cell wall polysaccharide synthesis (Ridley et al, 2001)
Summary
Pectin is structurally and functionally the most complex polysaccharide in plant cell walls (Mohnen, 2008). It is generally accepted that the amount and distribution of methyl groups affect the pectin matrix’s rheological properties, adhesive capacities, and resistance to degradation (Wolf et al, 2009, 2012) These changes affect plant growth and development through multiple processes, including organ initiation (Peaucelle et al, 2011), the maintenance of the stem’s mechanical strength (Hongo et al, 2012), and pollen formation (Francis et al, 2006). By observing calcium distribution and pectin esterification patterns in the cambial zones of poplar branches, the degree of HG methylesterification has been determined to vary from one cell type to another (Guglielmino et al, 1997) These reports indicate that the degree of pectin methylesterification in plants is under subtle regulation to maintain proper organogenesis and normal morphogenesis. Enzymatic activities that regulate the degree of HG methylesterification are likely to play major roles in the control of plant growth (Wolf et al, 2009)
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