Over-expression of HAP3b enhances primary root elongation in Arabidopsis.

HAPs, similar to Heme Activator Proteins (HAP) or nuclear factor-Y (NF-Y) in yeast and animals, play versatile roles in plant growth, development, and responses to environmental cues. HAP3b in Arabidopsis is a member in the HAP3 gene family and is involved in regulating flowering time through the long-day photoperiod pathway (Cai et al., 2007, Plant Physiol 145: 98-105). In this study, we report that overexpression of HAP3b enhances primary root elongation. Detailed analysis showed that HAP3b-overexpression did not affect the length of the root elongation zone and the cell length profiles in the elongation zone. Kinematic analysis indicated that root cells in HAP3b-overexpressors elongate faster than the cells in wild-type roots. Using GUS as a reporter gene, we showed that HAP3b is specifically expressed in the tip region of the root, where cell division and elongation occur. Our results provide evidence to support a role of HAP3b in regulation of root growth.

A putative CCAAT-binding transcription factor is a regulator of flowering timing in Arabidopsis.

Flowering at the appropriate time of year is essential for successful reproduction in plants. We found that HAP3b in Arabidopsis (Arabidopsis thaliana), a putative CCAAT-binding transcription factor gene, is involved in controlling flowering time. Overexpression of HAP3b promotes early flowering while hap3b, a null mutant of HAP3b, is delayed in flowering under a long-day photoperiod. Under short-day conditions, however, hap3b did not show a delayed flowering compared to wild type based on the leaf number, suggesting that HAP3b may normally be involved in the photoperiod-regulated flowering pathway. Mutant hap3b plants showed earlier flowering upon gibberellic acid or vernalization treatment, which means that HAP3b is not involved in flowering promoted by gibberellin or vernalization. Further transcript profiling and gene expression analysis suggests that HAP3b can promote flowering by enhancing expression of key flowering time genes such as FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1. Our results provide strong evidence supporting a role of HAP3b in regulating flowering in plants grown under long-day conditions.

Mutant identification and characterization of the laccase gene family in Arabidopsis.

Laccases, EC 1.10.3.2 or p-diphenol:dioxygen oxidoreductases, are multi-copper containing glycoproteins. Despite many years of research, genetic evidence for the roles of laccases in plants is mostly lacking. In this study, a reverse genetics approach was taken to identify T-DNA insertional mutants (the SALK collection) available for genes in the Arabidopsis laccase family. Twenty true null mutants were confirmed for 12 laccase genes of the 17 total laccase genes (AtLAC1 to AtLAC17) in the family. By examining the mutants identified, it was found that four mutants, representing mutations in three laccase genes, showed altered phenotypes. Mutants for AtLAC2, lac2, showed compromised root elongation under PEG-induced dehydration conditions; lac8 flowered earlier than wild-type plants, and lac15 showed an altered seed colour. The diverse phenotypes suggest that laccases perform different functions in plants and are not as genetically redundant as previously thought. These mutants will prove to be valuable resources for understanding laccase functions in vivo.