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Title: Recent advances in functional genomics for sugar beet (Beta vulgaris L.) improvement: progress in determining the role of BvSTI in pest resistance in roots

item Smigocki, Anna
item Haymes, Snezana

Submitted to: Sugar Tech
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2008
Publication Date: 3/26/2008
Citation: Smigocki, A.C., Haymes, S., Puthoff, D.P., Zuzga, S. 2008. Recent advances in functional genomics for sugar beet (Beta vulgaris L.) improvement: progress in determining the role of BvSTI in pest resistance in roots. Sugar Tech. 10(1):91-98, 2008.

Interpretive Summary: Disease and pest problems are responsible for decreases in production of sugar from sugar beet. Over 26 million tons of sugar beet valued at over 1.2 billion dollars are produced each year in the U.S. One of the most devastating insect pests of sugar beet is the sugar beet root maggot that is currently found in more than half of all U.S. sugar beet fields. To gain a better understanding of how plants protect themselves from insect attack, in our past studies we identified sugar beet genes that respond to sugar beet root maggot infestation in root maggot-susceptible and moderately resistant sugar beet varieties. One of the genes (BvSTI) was selected for further analysis to assess its effectiveness in controlling insect feeding. In this study, we report new findings on production of a model plant (Nicotiana benthamiana) that is genetically modified to overproduce the sugar beet gene (BvSTI) product. Preliminary results indicate that when insects feed on these plants they are smaller in size than insects that feed on the unmodified plants. These results suggest that the sugar beet gene may be useful for control of insect damage in plants other than sugar beet. Scientists will use this information to identify components of plant resistance mechanisms that will lead to new approaches for increasing pest and disease resistance in plants.

Technical Abstract: To gain knowledge of root resistance mechanisms in sugar beet, Beta vulgaris L., our laboratory has been studying the interaction of sugar beet with its most devastating insect pest, the sugar beet root maggot (SBRM; Tetanops myopaeformis Roder). Damage from SBRM infestations is a serious problem and current control measures rely on environmentally damaging insecticides. We recently reported root-specific gene expression incited by SBRM feeding in a moderately resistant F1016 and a susceptible parental F1010 line. A cDNA expressed sequence tag (EST) coding for a serine (trypsin-type) protease inhibitor (BvSTI) was identified and investigated further here. BvSTI shares sequence similarity with a root-specific tomato gene whose expression is induced by insect feeding. Since serine proteases comprise the major digestive enzymes in root maggot midguts, we hypothesize BvSTI may be involved in resistance. To elucidate the functional role of BvSTI, its coding region was fused to the CaMV 35S promoter and constitutively expressed in sugar beet hairy roots. A 2 to 4-fold higher level of trypsin inhibitory activity was detected in independently derived F1010 root lines. In this study, we report new findings on the regeneration of Nicotiana benthamiana plants that express the BvSTI gene. Using a polyacrylamide gel assay, new trypsin-like PI activity was detected in BvSTI-N. benthamiana plants. Since SBRM cannot be reared in vitro, two other insects that utilize serine digestive proteases, fall armyworm (Spodoptera frugiperda) and tobacco hornworm (Manduca sexta), were screened for resistance. To date, we demonstrated that 1) fall armyworm will feed on sugar beet hairy roots and 2) tobacco hornworm fed BvSTI-N. benthamiana leaves were smaller than the controls. These results suggest that BvSTI may contribute to the moderate resistance of F1016 roots to SBRM. Functional analysis of additional ESTs will further support efforts to characterize the components of sugar beet root resistance mechanisms.