Abstract
Flavonols, a subclass of flavonoids, have crucial roles in UV protection and modulation of flower color. They are known to have roles in leguminous plants-rhizobia symbiosis. Recently, it was also suggested that they act as auxin transport regulators during nodulation. We identified the genes of Lotus japonicus coding flavanone 3-hydroxylase (FHT1 and FHT2) or flavonol synthase (FLS1, FLS2 and FLS3) to uncover the role of flavonols during nodule development. Their expression levels, except for FLS3, were transiently up-regulated at 2 days after inoculation with wild-type Mesorhizobium loti, whereas they kept increasing after 4 days with nodA or nodD disruption mutants. These results suggest that the expression of the genes coding biosynthetic enzyme of flavonol was suppressed by Nod factor and induced by unidentified factor derived from M.loti. The expression of GUS gene driven by FHT1 or FLS1 promoter clarified that FHT1 is expressed in various organs, and that FLS1 is specifically expressed in shoot and root apices. Furthermore, we are now preparing FLS1 transgenic hairy roots to examine the impact of the modification of flavonol biosynthesis on root nodulation.
