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Title: PROGRESS TOWARDS AN UNDERSTANDING OF THE MECHANISMS THAT REGULATE ABSCISSION.

Author
item Tucker, Mark
item Hong, Seung Beom
item KALAITZIS, PANAGIOTIS - ARS
item ZHOU, D - ARS
item NATH, P. - ARS

Submitted to: Acarology International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/15/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Abscission (organ separation) reduces the yield of agriculturally important crops. Our goal is to genetically engineer plants with economically beneficial abscission characteristics. For example, the yield of soybean may be increased by reducing premature abscission of fertile flowers and seed pods. Several different approaches are being used. One approach is to identify and characterize DNA fragments that are responsible for regulating the accumulation of protein during leaf, flower and fruit abscission. We have shown that a fragment of bean DNA contains information that regulates the hormonal induction of a reporter gene when put into tomato. The sequence of this DNA fragment from bean also is highly conserved in soybean. In addition to bean and soybean, we are also studying abscission in tomato and have identified several genes that are specifically expressed during tomato abscission. Another approach is to identify genes in the plant's hormone signaling pathway that determines the onset of abscission. Towards this end, we have identified several genes that encode sensory proteins involved in the detection of the plant hormone, ethylene. The results reported in this manuscript will be useful to other researchers studying abscission and hormonal regulation in plants.

Technical Abstract: Abscission (organ separation) correlates with the de novo accumulation of mRNA for several cell wall hydrolases. Genomic clones encoding a bean abscission cellulase (BAC) and a soybean abscission cellulase (SAC) were identified and their sequences compared. Of special interest is the region between -1 and -200 bp in the BAC promoter which is highly conserved in the SAC gene. Particle gun bombardment with a BAC promoter construct containing 210 bp of BAC sequence 5 to the transcription start site was sufficient to drive abscission-specific and ethylene- and auxin-regulated transient expression in bean. A conserved ACGT sequence, a putative bZIP type DNA binding element, is found in both the BAC and SAC sequences at -106 bp. Mutations introduced into the ACGT element reduced reporter gene expression by approximately 80%. Abscission is regulated by ethylene. In a separate project, we have identified a tomato cDNA clone, TAE1, that is complementary to the Arabidopsis ETR1 gene, a putative ethylene receptor gene. A mutation has been introduced into the TAE1 sequence to mimic the dominant ethylene insensitive etr1-1 mutation. This sequence has been fused to an abscission-specific promoter and transformed into tomato to study its potential for genetic inhibition of abscission.