Expression and evolution of functionally distinct haemoglobin genes in plants.

Area of Science:

• Plant molecular biology
• Evolutionary biology
• Genomics

Background:

• Non-symbiotic hemoglobins (Hb) are found in plants, but limited sequences hindered evolutionary analysis.
• Understanding plant Hb evolution requires a broader dataset, including diverse species and classes.

Purpose of the Study:

• To present new non-symbiotic Hb sequences from various plant species, including non-vascular plants.
• To conduct a molecular phylogenetic analysis of known non-symbiotic and symbiotic Hb genes.
• To investigate the distinct functions of two non-symbiotic Hb classes in Arabidopsis.

Main Methods:

• Sequencing of nine new non-symbiotic Hb genes from cotton, Citrus, tomato, sugar beet, canola, Marchantia polymorpha, and Physcomitrella patens.
• Molecular phylogenetic analysis incorporating all known non-symbiotic and selected symbiotic Hb genes.
• Analysis of gene expression patterns in transgenic Arabidopsis using promoter-GUS reporter fusions.

Main Results:

• Confirmed two distinct classes of non-symbiotic Hb genes (class 1 and class 2) in dicots; only class 1 detected in monocots.
• Symbiotic Hbs from legumes/Casuarina relate to class 2, while Parasponia Hb groups with class 1, suggesting two independent symbiotic Hb recruitments.
• Arabidopsis class 1 (GLB1) and class 2 (GLB2) genes show distinct expression patterns and inducibility, indicating functional divergence.

Conclusions:

• Dicots likely possess both class 1 and class 2 non-symbiotic Hb genes, whereas monocots appear to have only class 1.
• The distinct evolutionary origins and expression patterns of non-symbiotic Hbs suggest specialized roles within plants.
• Further research into plant Hb functions is warranted based on observed expression divergence.