|Joost, Oscar - TEXAS A&M UNIVERSITY|
|Bianchini, Graciela - TEXAS A&M UNIVERSITY|
|Benedict, C - TEXAS A&M UNIVERSITY|
|Magill, Clint - TEXAS A&M UNIVERSITY|
Submitted to: Plant Microbe Interactions and Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 9, 1995
Publication Date: N/A
Interpretive Summary: Resistance to Verticillium wilt in the cotton cultivars is related to a rapid accumulation of phytoalexins (antibiotics) that kill the fungal pathogen. Understanding the genetic bases of this rapid response should facilitate the cloning and transfer of responsible genes. In the present study 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) was identified as the earliest enzyme in the biosynthesis of phytoalexins that correlates with the speed of phytoalexin accumulation. The partial gene controlling HMGR synthesis was cloned and used to show that increases in HMGR enzyme activity were correlated with increases of HMGR messenger RNA. This indicates that HMGR gene induction is required for phytoalexin synthesis. Cotton genomes contained 5-9 copies of HMGR genes. This study provides basic information needed to improve disease resistance in cotton using molecular techniques.
Technical Abstract: Gossypium barbadense cottons are typically more resistant to wilt pathogens than are cultivars of Gossypium hirsutum. Both species make terpenoid phytoalexins in response to infection, implicating isoprenoid biosynthesis as a factor in resistance. Conserved regions in plant 3- hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), the first enzyme in the terpene biosynthesis pathway, were used to design PCR primers for cloning a fragment of a cotton HMGR gene. The clone was used as a probe on Northern blots to show than induction of HMGR mRNA following introduction of Verticillium dahliae spores into the vascular system is much more rapid in Seabrook Sea Island, a resistant G. barbadense cotton, than it is in Rowden, a susceptible G. hirsutum. The amount of HMGR mRNA returned to near control levels in 4 days in the former variety but continued to accumulate in the latter. Specific enzyme activity of HMGR also increased more rapidly in stele extracts of Seabrook Sea Island than Rowden.