Submitted to: Biochimica et Biophysica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2002
Publication Date: 3/1/2003
Citation: ZHANG, X., JENKINS, J.N., CALLAHAN, F.E., CREECH, R.G., SI, Y., MCCARTY JR, J.C., SAHA, S., MA, D. MOLECULAR CLONING, DIFFERENTIAL EXPRESSION, AND FUNCTIONAL CHARACTERIZATION OF A FAMILY OF CLASS I UBIQUITIN-CONJUGATING ENZYME (E2) GENES IN COTTON (GOSSYPIUM). BIOCHIMICA ET BIOPHYSICA ACTA. 2003. v.1625.p.269-279. Interpretive Summary: Five genes from cotton that are involved in protein degradation have been identified. This is a process whereby proteins no longer needed by the plant are degraded and the amino acids are reused by the plant. Many of these proteins are involved in regulatory, transcription, and signal transduction in plants. The derived amino acid sequences of the five closely related cotton genes that code for ubiquitin-conjugating enzymes are 77 to 79% identical to yeast genes ScUBC4 and ScUBC5. Two genes, GhUBC1 and GhUBC2, are from the tetraploid, Gossypium hirsutum, GaUBC1, GtUBC2, and GrUBC2 were identified from the diploid species, G. arboreum, G. thurberi, and G. raimondii. GhUBC1 and GhUBC2 are individually present in the A and D subgenomes of G. hirsutum. The transcript level of GhUBC1 and GhUBC2 increased significantly in leaves and flowers at senescence, suggesting that they may play a role in the degradation of target protein that functions in the delay of the senescence in cotton. These two are also present at high levels in very young leaves, the apical part of lateral roots, and in elongating fibers. These two can substitute for ScUBC4 and ScUBC5 function in complementation experiments with the double mutant of yeast. This provides additional evidence that the function of these two genes in cotton is similar to the two yeast genes.
Technical Abstract: Two cDNAs and their corresponding genes (GhUBC1 and GhUBC2) encoding ubiquitin-conjugating enzymes (E2s) have been cloned and characterized from allotetraploid cotton, Gossypium hirsutum ((AD)1 genome). Three additional E2 genes (GaUBC1, GtUBC2, and GrUBC2) have also been identified from diploid cottons, Gossypium arboreum (A2 genome), Gossypium thurberi (D1 genome), and Gossypium raimondii (D5 genome), respectively. The derived amino acid sequences of the five closely related cotton E2s are 77-79% identical to yeast ScUBC4 and ScUBC5. The GhUBC1/2 gene family is composed of two numbers, and genomic origin analysis indicates that GhUBC1 and 2 are individually present in the A and D subgenomes of G. hisutum. The transcript levels of GhUBC1/2 increased significantly in leaves and flowers at senescence, suggesting that GhUBC1/2 may play a role in the degradation of target proteins that function in the delay of the senescence program. Correlated with high auxin content and auxin-associated effects, GhUBC1/2 are also highly expressed in the youngest leaves, the apical part of lateral roots, and elongating fibers. Genetic complementation experiments revealed that GhUBC1 and 2 can substitute for the function of ScUBC4 and 5 required for the selective degradation of abnormal and short-lived proteins in a yeast ubc4ubc5 double mutant.