Members of theLBDFamily of Transcription Factors Repress Anthocyanin Synthesis and Affect Additional Nitrogen Responses inArabidopsis   

Abstract

Nitrogen (N) and nitrate (NO 32 ) per se regulate many aspects of plant metabolism, growth, and development. N/NO 3 2 also suppresses parts of secondary metabolism, including anthocyanin synthesis. Molecular components for this repression are unknown. We report that three N/NO 3 2 -induced members of the LATERAL ORGAN BOUNDARY DOMAIN (LBD) gene family of transcription factors (LBD37, LBD38, and LBD39) act as negative regulators of anthocyanin biosynthesis in Arabidopsis thaliana. Overexpression of each of the three genes in the absence of N/NO 3 2 strongly suppresses the key regulators of anthocyanin synthesis PAP1 and PAP2, genes in the anthocyanin-specific part of flavonoid synthesis, as well as cyanidinbut not quercetin-or kaempferol-glycoside production. Conversely, lbd37, lbd38, or lbd39 mutants accumulate anthocyanins when grown in N/NO 3 2 -sufficient conditions and show constitutive expression of anthocyanin biosynthetic genes. The LBD genes also repress many other known N-responsive genes, including key genes required for NO 3 2 uptake and assimilation, resulting in altered NO 3 2 content, nitrate reductase activity/activation, protein, amino acid, and starch levels, and N-related growth phenotypes. The results identify LBD37 and its two close homologs as novel repressors of anthocyanin biosynthesis and N availability signals in general. They also show that, besides being developmental regulators, LBD genes fulfill roles in metabolic regulation. INTRODUCTION Nitrogen (N) and nitrate (NO 32 ) itself regulate many aspects of plant metabolism, growth, and development. These include NO 3 2 uptake and assimilation (Crawford, 1995;Lejay et al., 1999), starch and organic acid metabolism (Scheible et al., 1997a), secondary metabolism (e.g., anthocyanin production) Fritz et al., 2006), germination (Alboresi et al., 2005), root architecture (Zhang et al., 1999), root and shoot development (Scheible et al., 1997b), leaf expansion (Walch-Liu et al., 2000), stomatal opening (Guo et al., 2003), flowering (Bernier et al., 1993), seed set, and senescence (Crawford, 1995;Stitt, 1999;Crawford and Forde, 2002). Some molecular components involved in regulation of these N/NO 3 2 responses in Arabidopsis thaliana have been described. The MADS box transcription factor (TF) ARABIDOPSIS NITRATE REGULATED1 (ANR1) was found to act as regulator of systemic NO 3 2 repression and localized NO 3 2 stimulation of lateral root growth (Zhang and Forde, 1998). NITRATE TRANSPORTER1.1 (NRT1.1) was subsequently shown to act upstream of ANR1 in the signaling pathway triggering lateral root growth and root colonization of NO 3 2 -rich patches (Remans et al., 2006) and to regulate expression of the high-affinity NO 3 2 transporter NRT2.1 (Muñ os et al., 2004). Also, NRT2.1 is suspected to repress lateral root initiation in response to nutritional cues by acting either as a NO 3 2 sensor or signal transducer (Little et al., 2005). Recently, a CBL-interacting protein kinase, CIPK8, was shown to regulate parts of the primary NO 3 2 response, incl...

The Lateral Organ Boundaries Domain Transcription Factor LBD20 Functions in Fusarium Wilt Susceptibility and Jasmonate Signaling in Arabidopsis

“…The C motif containing four cysteines is conserved in all LBD proteins and is predicted to form a DNA-binding zinc finger, while the lessconserved Leu-zipper-like motif is predicted to form a coiled-coil motif involved in homodimerization or other protein-protein interactions (Shuai et al, 2002;Majer and Hochholdinger, 2011). Nuclear localization and DNA-binding activity shown for some members suggests LBD proteins function as transcription factors (Shuai et al, 2002;Husbands et al, 2007;Naito et al, 2007;Rubin et al, 2009). Indeed, the LOB domain is sufficient for DNA-binding activity, and Husbands et al (2007) found several LBD members could bind a 6-bp consensus motif (G)CGGC(G), termed the LBD motif, with a broader sequence of A/T C/T GCGGCG C/T/G A/G A/T.…”

“…The LBD family has previously mainly been studied in regard to plant development with roles in defining the boundaries between organs (Shuai et al, 2002;Majer and Hochholdinger, 2011;Feng et al, 2012). Other LBDs have been shown to have functions in the regulation of nitrogen metabolism and anthocyanin biosynthesis (Rubin et al, 2009). Functions of LBD20 were previously unknown, and our results demonstrate LBD20 is the first member of the LBD family shown to have a role in JA signaling and plant-pathogen interactions.…”

Arabidopsis NIN-like transcription factors have a central role in nitrate signalling

“…As NIN, which is necessary for symbiosis between legumes and nitrogen fixing bacteria, had been proposed as a putative transcription factor 20 , NLP7 is also speculated to be a regulatory protein associated with nitrogen assimilation. The LBD genes are also proposed to encode transcription factors associated with nitrate-responsive gene expression, because overexpression of LBD37, LBD38 or LBD39 represses the expressions of nitrate transporter and NR genes in Arabidopsis 21 . Another Arabidopsis gene, GNC, has also been identified as a nitrateinducible gene encoding a putative transcription factor of the GATA family 22 .…”

Nitrate foraging by Arabidopsis roots is mediated by the transcription factor TCP20 through the systemic signaling pathway

“…Within minutes, primary nitrate response genes, including members of the nitrate transporter families NRT1 and NRT2 and the nitrate and nitrite reductase genes NIA1, NIA2, and NiR, are induced. These responses are mediated by signaling pathways that include the nitrate transceptor NRT1.1 (13,14), two kinases (CIPK8 and CIPK23) (13,15), and the transcription factors NLP6/7 (16)(17)(18), LBD37/38/39 (19), and SPL9 (12).…”