Characterization of Lotus japonicus mutant plants deficient in phytoglobins

Abstract

In plants, symbiotic hemoglobins occur only in the nodules of legumes (leghemoglobins; Lbs), actinorhizal plants, and Parasponia. These hemoglobins transport a low, steady concentration of O2 to the N2-fixing bacteroids. In contrast, nonsymbiotic hemoglobins or phytoglobins (Glbs) are expressed in most plant organs, from seeds to flowers and fruits (Bustos-Sanmamed et al., 2011). Based on phylogenetic analyses and biochemical properties, Glbs can be grouped in three classes. The genome of Lotus japonicus encodes five Glbs: two class 1 (Glb1-1 and Glb1-2), one class 2 (Glb2), and two class 3 (Glb3-1 and Glb3-2). The functions of Glbs are largely unknown. To gain information, we phenotyped glb knockout mutants from the LORE1 collection (Malolepszy et al., 2016). Phenotypes were examined in nodulated plants grown in plates for 4-5 weeks on Jensen medium. The plants were then transferred to pots and the phenotypes were analyzed again at 8 weeks and at the flowering and fruiting stages. Nodulated plants of the glb1-1 mutant were smaller and had fewer nodules than the WT. The glb1-2 plants showed no growth alterations but delayed flowering, although they had many flowers that did not produce pods. The glb2 mutant showed a reduction in size and nodule number, as well as a delay in flowering. Finally, the glb3-2 mutants showed reduced shoot and root weights, delayed flowering, and enhanced production of flowers and pods.