Storage Root Initation

1415. Anatomical study of sweetpotato storage root initiation and formation in the leading Israeli variety Georgia Jet (back)

Yanir Kfir¹, Etan Pressman¹, Levia Althan¹, Rachel Shaked¹ , Amnon Schwartz², and Nurit Firon¹*
¹Institute of Plant Sciences, The Volcani Center, Agricultural Research Organization, P.O.Box 6, Bet Dagan, 50250, Israel
² Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, 76-100, Israel

The most economically important physiological process in sweetpotato production is storage root (SR) development. Initially white adventitious roots develop, and some of these roots subsequently undergo sudden changes in their growth pattern and develop into SRs. Storage root production is inconsistent from plant to plant; some plants have few or no SRs while others have four or more marketable ones. Substantial information is missing with relation to the factors that promote formation of sweetpotato SRs in general and in the most common variety in Israel, 'Georgia-Jet', in particular. Morphological and anatomical studies indicate that the SR induction phase in 'Georgia-Jet' is marked by pink pigmentation in the epidermis and by formation of anomalous cambium cells around xylem vessels, respectively, appearing between 3-4 weeks after planting. The effect of environmental factors on induction of SR formation and SR development will be discussed. More than 5-fold increase in starch levels is detected in 'Georgia-Jet' roots at four weeks after planting as compared to roots sampled at three weeks after planting. The accumulated data are currently used for identifying genes specific to storage root formation through expression profiling of roots sampled before and during the SR induction phase.

1445. Transcription profiles of fibrous roots and storage roots of sweetpotato.(back)

C.M. McGregor and D.R. La Bonte*

School of Plant, Environmental, and Soil Sciences
Lousiana State University AgCenter, Baton Rouge, LA 70803

Storage root formation is the most economically important process in sweetpotato [Ipomoea batatas (L.) Lam.] development. In an effort to understand this process, RNA from fibrous and storage roots of the cultivar ‘Jewel’ were harvested six weeks after planting and hybridized to the ARCS_SP02 sweetpotato microarray. The array contains 1,060 features originating from a sweetpotato leaf library and 1,728 features from a storage root library. Differential expression was observed for 966 expressed sequence tags. A variety of transcription-related genes were differentially expressed including a MADS-box gene and homeo-box genes. Our results also indicate a possible role for auxin and other hormones, such as gibberellin, ethylene and jasmonic acid in storage root development.

1530. Functional characterization of genes related to storage root development in sweetpotato (back)

Seol Ah Noh and Jung Myung Bae*
School of Life Sciences and Biotechnology, Korea University, Seoul, KOREA 136-701

We previously isolated EST clones from sweetpotato (Ipomoea batatas cv. Jinhongmi) cDNA library constructed with young storage root. Expression analysis of the EST clones with various tissues of sweetpotato identified SRD (Storage Root Development) genes involved in the storage root development. Genomic Southern blot analyses determined gene copy numbers of SRD genes in sweetpotato genome and in situ hybridization with cross-sections of storage root revealed localization of SRD genes expression in storage root tissues. To functionally characterize the SRD genes, we isolated full-length cDNA clones of the SRD genes, inserted them into the pMBP1 binary vector in sense- and antisense-direction and transformed sweetpotato using particle bombardment. Insertion of transgenes was identified using PCR amplification and alteration in the expression of target genes was investigated using RT-PCR. Microscopic observation of fibrous root of in vitro-cultured transgenic sweetpotatoes revealed morphological alterations in the transgenic sweetpotatoes. Growth of storage root was compared between non-transgenic and transgenic sweetpotato plants. These results suggested possible roles of the SRD genes in the storage root development in sweetpotato.

1600. Class I knotted1-like homeobox genes are expressed in storage roots of sweetpotato (back)

Masaru Tanaka^1*, Nakao Kato¹, Hiroki Nakayama¹, Yasuhiro Takahata1, Makoto Nakatani²

¹National Agricultural Experiment Station for Kyushu Okinawa Region, Miyakonojo, Miyazaki 885-0091, Japan; ²Agriculture, Forestry and Fisheries Research Council Secretariat, MAFF, Chiyoda-ku, Tokyo 100-8950, Japan

Class I knotted1-like homeobox (KNOXI) genes encode transcription factors belong to the TALE superclass of homeobox proteins. In many plants, KNOXI genes are specifically expressed around the shoot apex and play important roles in meristem maintenance and proper organ patterning by regulating cytokinin and gibberellin biosynthesis. Recently, we have isolated four KNOXI cDNA, named Ibkn1 to Ibkn4, expressed in storage roots of sweetpotato. Phylogenetic analysis showed that Ibkn1 is homologous to the SHOOTMERISTEMLESS genes of Arabidopsis, while Ibkn2 and Ibkn3 are homologous to the BREVIPEDICELLUS gene. Ibkn4 was homologous to the KNAT2 and KNAT6 gene of Arabidopsis. Semi-quantitative RT-PCR analysis showed that the expression of Ibkn1, Ibkn2 and Ibkn4 are upregulated in storage roots compared to fibrous roots in all sweetpotato cultivar analyzed, suggesting their involvements in the storage root development. In storage roots, these KNOXI genes showed slightly different expression patterns. Putative functions of these KNOXI genes in storage root development will be discussed.