A RAV-like transcription factor controls photosynthesis and senescence in soybean

A cDNA library enriched for mRNAs encoding ESTs that increased in abundance during short days was constructed by SSH from leaf tissues of a photoperiod sensitive soybean. The proteins predicted to be encoded by the mRNAs were inferred to be involved in diverse functions. A full-length mRNA that encoded a soybean ortholog of the transcription factor RAV was isolated by RACE, containing an open reading frame of 1,056 bp. The GmRAV protein included an AP2/ERF domain and a B3 domain. GmRAV mRNA abundance was increased in SDs following leaf treatments with ABA and decreased following BR treatment. Transgenic tobacco overexpressing GmRAV showed morphological and physiological alterations such as slower plant growth rate (dwarfing), reduced root elongation, delayed flowering time and reduced photosynthetic rate, reduced chlorophyll contents in leaves. Therefore GmRAV may be a negative regulator acting on both photosynthesis and growth. Transgenic tobacco also showed accelerated senescence with both dark and ABA treatments versus the longer longevity compared to the wild type in LDs. The analyses of soybean leaf, root and stem organs showed that GmRAV mRNA abundances were higher in SDs than in LDs. Therefore, the enhanced expression of GmRAV in SDs compared to LDs may have caused the inhibited growth of soybean leaf, root and stem.