Texas A&M University

Abscisic acid regulation of C1 transcription

--Nam Paek, Dong G. Bai, Clint W. Magill, B. Greg Cobb and J. D. Smith

In the appropriate genetic background, all of the viviparous maize mutants except vp1 have colored aleurone. However, kernel blocks cultured in vitro on medium containing fluridone, which inhibits phytoene desaturase, are white with colorless aleurone.

Anthocyanin synthesis in maize aleurone requires C1 transcription (Cone, K et al., PNAS 83:9631-9635, 1985), but C1 is not transcribed in the absence of Vp1 mRNA (McCarty, DR et al., Plant Cell 1:523-532, 1989).

We used an ACR58552 stock (A1 A2 C1 C2 Bz1 Bz2 R Pr Vp1) to determine if transcription of Vp1 or C1 was affected by abscisic acid (ABA). Ears were harvested at 5 DAP and kernel blocks were cultured on media ± fluridone. ABA levels ±SE determined from 15 DAP embryos cultured without fluridone were 138.4±35.3 pg ABA embryo-1 and 1.5±0.2 pg ABA embryo-1 when cultured with fluridone. Antisense RNA transcripts from Vp1 cDNA and from C1 cDNA were used to test for hybridization signals with their respective mRNA from aleurone tissues of 13, 15 and 20 DAP kernels cultured with and without fluridone.

Hybridization signals were observed for Vp1 mRNA at all ages for kernels cultured with or without fluridone. However, C1 mRNA hybridization signals were detected only for kernels that were cultured without fluridone.

Vp1 transcription is not affected by ABA and we have been unable to identify any association of ABA with the protein encoded by Vp1. Thus, ABA appears to act as an independent transcriptional factor involved in the regulation of C1 transcription. This would explain why ACR58552 kernels cultured on medium with fluridone are colorless, but they have colored aleurone on medium containing both fluridone and ABA (Smith, JD and Cobb, BG, MNL 63:57-58, 1989). In cultured kernels both the intensity and time of anthocyanin expression vary with ABA levels in the media, which suggests that ABA is the effective regulator of anthocyanin expression in maize aleurone when Vp1 and C1 are present.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors

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