Pectin Metabolism Influences Phloem Architecture and Flowering Time in Arabidopsis Thaliana.

Cell wall matrices undergo continuous remodeling during plant growth and development. The methyl- and de-methyl-esterification of pectic homogalacturonan dynamically influence the physicochemical and mechanical properties of cell walls, and consequently regulate organ morphogenesis. Phloem plays a crucial role in the transport of photoassimilates and other organic molecules from source to sink tissues, and the walls of phloem cells are rich in pectins. However, how pectin metabolism orchestrates phloem architecture and function is unclear. This work demonstrates that the methyl-esterification status and subsequent degradation of pectic homogalacturonan affect flowering time by modulating phloem development and transport capacity, which control the transport of a mobile florigen, FLOWERING LOCUS T protein, in the phloem stream. During this process, auxin signaling is stimulated by pectin de-methyl-esterification to influence vasculogenesis. Together, this data provide new insights into the mechanisms by which pectin chemistry is coordinated with auxin signaling to mediate phloem development, long-distance transport and flowering time.