Abstract
Flavonoids are specialized compounds widely distributed and with diverse functions throughout the plant kingdom and with several benefits for human health. In particular, flavonols, synthesized by flavonol synthase (FLS), protect plants against UV-B radiation and are essential for male fertility in maize and other plants. We have recently characterized a UV-B inducible ZmFLS1, corresponding to the first to be described in monocot plants. Interestingly, the new assembly of the B73 maize genome revealed the presence of a second putative FLS gene (ZmFLS2), with very high identity with ZmFLS1. ZmFLSs expression was analyzed in different maize tissues, and by combining electrophoretic mobility shift assays and transient expression experiments, we show that both genes are direct targets of anthocyanin (C1/PL1 + R/B) and 3-deoxy flavonoid (P1) transcriptional regulators. ZmFLS expression analyses show higher levels of both transcripts in high altitude landraces than inbred lines, and both genes are regulated by UV-B radiation in all lines analyzed. Moreover, the high sequence conservation of the ZmFLS promoters between maize lines suggests that the differences observed in ZmFLS expression are due to allelic variations in the transcription factors that regulate their activities. Finally, we generated pFLS1::FLS1-RFP transgenic plants and analyzed ZmFLS1 expression in different maize tissues; we found that this enzyme is localized in the ER and the perinuclear region.
Highlights
Flavonoids are widely distributed plant metabolites with diverse biological functions
Unlike what is found in maize, the two sorghum flavonol synthase (FLS) genes are located in different chromosomes [4 and 3 for SbFLS1 (Sb04g034240) and SbFLS2 (Sb03g002040), respectively] and SbFLS1 is more closely related to ZmFLSs (87–89% identity) than to SbFLS2 (72% identity), which is consistent with synteny analyses
The recently completed maize genome sequence shows that two FLS genes are present in the B73 line, resulting from complete genome duplication during evolution (Schnable et al, 2009)
Summary
Flavonoids are widely distributed plant metabolites with diverse biological functions. The most abundant and widespread subgroup of flavonoids, play important functions in plant physiology, growth, and development, including the modulation of basipetal auxin transport in Arabidopsis (Brown et al, 2001; Peer et al, 2004; Kuhn et al, 2011; Lewis et al, 2011), attraction of and defense against insects (Gronquist et al, 2001), pollen fertility (Mo et al, 1992; Taylor and Jorgensen, 1992; Ylstra et al, 1994; Taylor and Hepler, 1997), and UV-B protection (Solovchenko and Schmitz-Eiberger, 2003; Jaakola et al, 2004; Stracke et al, 2007, 2010a; Kusano et al, 2011). It has been demonstrated that the bZIP transcription factor long HYpocotyl (HY5), an important participant in the UV-Binduced signal transduction cascade mediated by UVR8, regulates the expression of PFG1/MYB12 under UV-B radiation (Stracke et al, 2010a). AtFLS1 and other genes encoding enzymes involved in flavonol biosynthesis are targets of these regulators (Mehrtens et al, 2005; Stracke et al, 2007, 2010a)
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