Abstract
When roots encounter localized source of nitrate, lateral root growth is stimulated. Studies with Arabidopsis indicate a MADS-box transcription factor, ANR1, is a key regulator of this mechanism. We have been characterizing AGAMOUS-LIKE 21 (AGL21) which belongs to this gene family. However, unlike ANR1, AGL21 was suggested to function when supply nitrogen was limited. The agl21 mutants had reduced lateral root growth compared to the wild-type plants when nitrate concentrations were 0.03 - 0.1 mM or when 0.1 mM glutamine was substituted for nitrate as an alternative nitrogen source. The overexpression of AGL21 was able to restore the growth of lateral roots in the agl21 mutant both in the presence and absence of nitrate. Consistent with AGL21's role in regulating lateral root growth, the AGL21 promoter activity was present specifically in the root tips of the primary and lateral roots. In Arabidopsis, AGL16, AGL17, and AGL21 are highly homologous to ANR1. An agl17 agl21 anr1 triple mutant was constructed to investigate the individual roles of ANR1 homologues whose transcripts were mainly found in roots. The results will be discussed with the analysis of promoter-GFP plants.
