Increase in vascular pattern complexity caused by mutations in LHY and CCA1 in Arabidopsis thaliana under continuous light

Abstract

Circadian rhythms in Arabidopsis thaliana (Arabidopsis) are controlled by clock components such as LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1). Plants with mutations in both LHY and CCA1 (lhy;cca1) show a wavy leaf phenotype under continuous light (LL). The circadian clock regulates both the biosynthesis and signaling of plant hormones, including auxin. Auxin plays a key role in vascular pattern formation in leaves. For example, plants with mutations in either VASCULAR NETWORK DEFECTIVE 3 (VAN3) or FORKED 1 (FKD1) exhibit reduced complexity in their leaf vascular patterns. However, the molecular mechanism underlying the decrease in flatness of lhy;cca1 leaves under LL has not been elucidated. To address this question, the leaf vascular patterns of lhy;cca1 were compared with those of wild-type, van3, and fkd1 plants under LL. As reported previously, the numbers of areoles and branch points in van3 and fkd1 plants grown for 14 days under LL were much lower than those of wild-type plants. In contrast, the numbers of free ends, areoles, and branch points increased in lhy;cca1. This is the first demonstration of Arabidopsis mutants with increased vascular pattern complexity. Our results suggest that the circadian clock plays a key role in controlling the vascular pattern of leaves.