Arabidopsis MYST6 encodes a rhamnogalacturonan lyase that modulates root growth
In the plant primary cell wall, the cellulose-xyloglucan network, the main load-bearing network, is embedded in and coextensive with a pectin network of undefined function in cell growth. Rhamnogalacturonan-I (RG-I) is a key component of the pectin network. Rhamnogalacturonan lyases (RG-lyases) have previously been identified as enzymes secreted by plant pathogens to degrade the plant cell wall. In this study, AtMYST6, belonging to the 7-member MYST gene family in Arabidopsis, has been identified as an endogeneous plant RG-lyase. Genetic modification of the expression levels of MYST6 change total RG-lyase activity and also RG-I structure. Homozygous T-DNA insertional mutants have short root hairs, reduced root growth, and a conditional early shoot senescence phenotype. RNAi-knockdown lines that specifically reduce MYST6 transcript levels partly phenocopy the root growth phenotypes but do not senesce early. The mutant phenotypes are rescued by expression of MYST6 under control of its native promoter. Expression of p35S:: MYST6 in Col-0 increased root hair lengths, root hair density, and lateral root density with additional shoot phenotypes, including partial loss of apical dominance. Parallel analysis of gene expression by microarray with ATH1 genechips suggests that components of signal transduction pathways, including leucine-rich repeat transmembrane protein kinases and protein phosphatases type 2C are involved in the function of MYST6 in plant growth and development. The expression of MYST6 affects the cleavage of RG-I and may produce a novel signal molecule (lepidimoide), which may trigger signal pathways affecting cell division and organ growth.
McCann, Purdue University.
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