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The Arabidopsis MYB5 Transcription Factor Regulates Mucilage Synthesis, Seed Coat Development, and Trichome Morphogenesis

Song Feng Li, Olga Nicolaou Milliken, Hanh Pham, Reg Seyit, Ross Napoli, Jeremy Preston, Anna M. Koltunow and Roger W. Parish
The Plant Cell
Vol. 21, No. 1 (Jan., 2009), pp. 72-89
Stable URL: http://www.jstor.org/stable/40537462
Page Count: 18
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Arabidopsis MYB5 Transcription Factor Regulates Mucilage Synthesis, Seed Coat Development, and Trichome Morphogenesis
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Abstract

The Arabidopsis thaliana MYB5 gene is expressed in trichomes and seeds, including the seed coat. Constitutive expression of MYB5 resulted in the formation of more small trichomes and ectopic trichomes and a reduction in total leaf trichome numbers and branching. A myb5 mutant displayed minimal changes in trichome morphology, while a myb23 mutant produced increased numbers of small trichomes and two-branched trichomes. A myb5 myb23 double mutant developed more small rosette trichomes and two-branched trichomes than the single mutants. These results indicate that MYB5 and MYB23 regulate trichome extension and branching. The seed coat epidermal cells of myb5 and myb5 myb23 were irregular in shape, developed flattened columellae, and produced less mucilage than those of the wild type. Among the downregulated genes identified in the myb5 seeds using microarray analysis were ABE1 and ABE4 (α/β fold hydrolase/esterase genes), MYBL2, and GLABRA2. The same genes were also downregulated in transparent testa glabrai (ttg1) seeds, suggesting that MYB5 collaborates with TTG1 in seed coat development. These genes were upregulated in leaves and roots by ectopically expressed MYB5. The MYBL2, ABE1, and ABE4 promoters were active in seeds, including seed coats, and the latter two also in trichomes. Models of the MYB5 regulatory networks involved in seed coat and trichome development are presented.

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