In recent years, Arabidopsis seed coat mucilage has been proved to
be an outstanding model system to study the biosynthesis, modification and
interaction of polys accharides, particularly pectin. Pectin is produced in the Golgi
apparatus and transferred with a high methyl-esterifiable status to the primary cell
wall, where it may be demethylesterified by pectin methylesterases (PMEs). The
functional properties of pectin are largely determined by the level and structure of
methylesterification, which then influence plant growth and development, stress
responses and so on. However, the regulatory mechanisms of pectin
demethylesterification remain mostly unexplored. Here, we show that a zinc-finger
transcription factor of Arabidopsis thaliana 5 (ZAT5) negatively regulates the pectin
demethylesterification in seed mucilage. A mutation of this ZAT5 transcription
factor led to a thinner seed coat mucilage layer and a decreased level of pectin
methylesterification caused by enhanced PME activity compared with the wild type. Further study indicates that ZAT5 negatively regulates the expression of 4 pectin
methylesterase (PME) genes, including PME5, HIGHLY METHYL ESTERIFIED
SEEDS (HMS)/PME6, PME12, and PME16, via binding their TGATCA-motif that
was identified in this study. Our results proved that ZAT5 negatively regulates
pectin demethylesterification. BEL1-Like Homeodomain (BLH) Transcription
Factor 2 and BLH4 are transcription factors that were previously identified to
positively modulate pectin demethylesterification by directly regulating PME58
expression. We demonstrated that ZAT5 and BLH2/4 physically interact and
antagonize each other’s ability in transcriptional regulation of target genes. It was
also proved that the mucilage phenotype of zat5-1 blh2 blh4 triple mutant seeds was
similar to that of the wild type. In conclusion, our work reveals that ZAT5 and
BLH2/4 antagonistically modulate downstream genes encoding PMEs to control
pectin demethylesterification in seed coat mucilage.