Differential Expression Patterns of Non-symbiotic Hemoglobins in Sugar beet (Beta vulgaris ssp. vulgaris).

Biennial sugar beet (Beta vulgaris spp. vulgaris) is a Caryophyllidae that has adapted its growth cycle to the seasonal temperature and day length variation of temperate regions. This is the first time a holistic study of the expression pattern of non-symbiotic hemoglobins (nsHbs) is being carried out in a member of this group and under two essential environmental conditions for flowering, namely vernalization and length of photoperiod. BvHbs were identified by sequence homology searches against the latest draft of the sugar beet genome. Three nsHbs (BvHb1.1, BvHb1.2, and BvHb2) and one truncated Hb (BvHb3) were found in the genome of sugar beet. Gene expression profiling of the nsHbs was carried out by quantitative PCR in different organs and developmental stages as well as during vernalization and under different photoperiods. BvHb1.1 and BvHb2 showed differential expression during vernalization as well as during long and short days. The high expression of BvHb2 indicates that it has an active role in the cell, maybe even taking over some BvHb1.2 functions, except during germination where BvHb1.2 together with BvHb1.1 -both class 1 nsHbs- are highly expressed. The unprecedented finding of a leading peptide at the N-terminus of BvHb1.1, an nsHb from higher plants together with its observed expression indicate that it may have a very specific role due to its suggested location in chloroplasts. Our findings open up new possibilities for research, breeding and engineering since Hbs could be more involved in plant development than previously was anticipated.