The over-expression of an alfalfa RING-H2 gene induces pleiotropic effects on plant growth and development

The alfalfa MsRH2-1 gene encodes a small protein with a RING-H2 motif and an N-terminal transmembrane domain. The transcript can be found in all tested plant organs, but roots and nodules show the highest levels of RH2-1 mRNA accumulation. Promoter-GUS fusion studies demonstrate that the activity of this gene is closely correlated with development of lateral roots ( in alfalfa and Arabidopsis) and symbiotic nodules ( in alfalfa). Although antisense-expressing alfalfa plants did not show a significantly different phenotype from the control plants, by contrast, when the level of the MsRH2-1 RNA was raised by introducing the coding part of the gene under the control of the CaMV promoter, both the transgenic alfalfa and Arabidopsis lines exhibited dramatic alterations in plant morphology, including shorter stature, increased apical dominance, leaf hyponasty, and inhibition of leaf venation and lateral root development. Moreover, nodulation of transgenic alfalfa roots was delayed and partially inhibited, and some of the Arabidopsis lines showed abnormal floral development. The nature of pleiotropic developmental phenotypes suggests a hormonal basis. The possible connection between MsRH2-1 function and substrate specific degradation via the ubiquitin pathway involved in auxin signaling is discussed.