| To investigate the genetic background and genes for rice root growth under water deficit, the natural drain-off system was used to simulate water deficit condition in this experiment. The root growth of upland rice, Azucena, under water deficit was compared with that under flooding condition. cDNA amplified fragment length polymorphism (cDNA-AFLP) analysis was used to examine gene expression profile in different root tissues during 72-h water deficit. The results are summarized as follows:1. Water deficit condition clearly affected root system architecture in upland rice. Different roots showed different responses to the water deficit condition. Short-duration of water deficit stimulated seminal and lateral root growth by accelerating seminal root elongation, promoting lateral root initiation and elongation, while reduced adventitious root elongation and number. Total root dry weight and the root-to-shoot ratio were increased under the water deficit condition.2. The elongation of cortical cells in the elongation zone was rapidly stimulated within 16h by the water deficit. cDNA-AFLP analysis was used to examine gene expression in seminal root tips (1cm) at four time points (4h, 16h, 48h and 72h) during the water deficit. One hundred and six unique genes induced by the water deficit were obtained. The expression patterns of 76% genes were confirmed by Northern blot analysis based on 21 selected genes representing different induced patterns.The 106 upregulated genes were composed of 60 function-known genes, 28 function-unknown genes and 18 novel genes. Sixty genes with known function were involved in transport facilitation, metabolism and energy, stress- and defense-related proteins, cellular organization and cell-wall biogenesis, signal transduction, expression regulator and transposable element, suggesting that seminal root tips undergo a complex adaptive process in response to the water deficit.Expression of 22 genes reached a maximum within 16 h of water-deficit treatment, which may be related to the root elongation stimulated by the water deficit attranscriptional level. Aquaporin (PIP2a), enolase in glycolysis, O-acetylserine (thiol)-lyase (OASTL) in S-assimilation, actin-depolymerizing factor (ADF), adenine phosphoribosyltransferase in the main adenine salvage pathway (APRT) were included. Five genes encode proteins involved in signal transduction and expression regulation, including calmodulin (CaM), MAP3K beta 1 protein kinase (MAP3K), 9-cis-epoxycarotenoid dioxygenase (NCED1) for ABA biosyntheses, a negative regulator of gibberellin signal transduction (SPY) and,an SR-related protein essential for spliceosome assembly (SART1). There were three genes for cell wall loosening proteins: endo-glucanase (EGase), xyloglucan endotransferase (XET) and expansin (OsEXP2). Five genes encode proteins involved in vesicle traffic, including vacuolar protein sorting protein (VPS33a), GTP-binding protein rabllb (Rab11b), two guanine nucleotide exchange proteins (GEP and GEP2) and autophagocytosis protein (APG). A simple model outlining the sequences of cellular events linking perception of a water-deficit signal to root elongation was proposed.3. cDNA-AFLP analysis was used to identify differentially expressed genes under water deficit condition in three root tissues: seminal root tips, lateral root zones and adventitious root primordial zones. One hundred and twelve specific bands were isolated and cloned. Fifty-eight transcript derived fragments (TDFs) showed differential expression in all three types of root tissues, 31 in both lateral root zones and seminal root tips, 10 in both seminal root tips and adventitious root primordial zones, 4 in both lateral root zones and adventitious root primordial zones, 7 only in seminal root tips and 1 only in lateral root zones. Northern blot analysis was carried out with random 21 clones to confirm their cDNA-AFLP expression patterns. The results obtained by cDNA-AFLP were in good agreement with those found in RNA gel blot analysis.Among the 1...
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