Three genetic systems controlling growth, development and productivity of rice (Oryza sativa L.): a reevaluation of the 'Green Revolution'.

The Green Revolution (GR-I) included worldwide adoption of semi-dwarf rice cultivars (SRCs) with mutant alleles at GA20ox2 or SD1 encoding gibberellin 20-oxidase. Two series of experiments were conducted to characterize the pleiotropic effects of SD1 and its relationships with large numbers of QTLs affecting rice growth, development and productivity. The pleiotropic effects of SD1 in the IR64 genetic background for increased height, root length/mass and grain weight, and for reduced spikelet fertility and delayed heading were first demonstrated using large populations derived from near isogenic IR64 lines of SD1. In the second set of experiments, QTLs controlling nine growth and yield traits were characterized using a new molecular quantitative genetics model and the phenotypic data of the well-known IR64/Azucena DH population evaluated across 11 environments, which revealed three genetic systems: the SD1-mediated, SD1-repressed and SD1-independent pathways that control rice growth, development and productivity. The SD1-mediated system comprised 43 functional genetic units (FGUs) controlled by GA. The SD1-repressed system was the alternative one comprising 38 FGUs that were only expressed in the mutant sd1 backgrounds. The SD1-independent one comprised 64 FGUs that were independent of SD1. GR-I resulted from the overall differences between the former two systems in the three aspects: (1) trait/environment-specific contributions; (2) distribution of favorable alleles for increased productivity in the parents; and (3) different responses to (fertilizer) inputs. Our results suggest that at 71.4 % of the detected loci, a QTL resulted from the difference between a functional allele and a loss-of-function mutant, whereas at the remaining 28.6 % of loci, from two functional alleles with differentiated effects. Our results suggest two general strategies to achieve GR-II (1) by further exploiting the genetic potential of the SD1-repressed and SD1-independent pathways and (2) by restoring the SD1-mediated pathways, or 'back to the nature' to fully exploit the genetic diversity of those loci in the SD1-mediated pathways which are virtually inaccessible to most rice-breeding programs worldwide that are exclusively based on sd1.

Clinimetric properties of relevant criteria for assessing writing and drawing orientation after right hemisphere stroke.

BACKGROUND: Writing and drawing orientation is rarely assessed in clinical routine, although it might have a potential value in detecting impaired verticality perception after right hemispheric stroke (RHS). Assessment tools and criteria must be conceived and validated. We therefore explored the clinimetric properties of a set of quantitative writing and drawing orientation criteria, their ranges of normality, and their tilt prevalence in RHS individuals. NEW METHODS: We asked 69 individuals with subacute RHS and 64 matched healthy controls to write three lines and to copy the Gainotti Figure (house and trees). We determined six criteria referring to the orientation of writing and drawing main axes: for writing, the line and margin orientations, and for drawing, the tree, groundline, wall, and roofline orientations. Orientations were measured by using an electronic protractor from specific landmarks positioned by independent evaluators. RESULTS: The set of criteria fulfilling all clinimetric properties (feasibility, measurability, reliability) comprised the line orientation of the writing and the wall and roofline orientations of the drawing. Writing and drawing tilts were frequent after RHS (about 30% by criterion). COMPARISON WITH EXISTING METHODS: So far, graphomotor orientation was mostly tested qualitatively and could not be objectively appreciated in absence of validated tools and criteria, and without ranges of normality. Writing and drawing tilts may now be assessed both in routine clinical practice and research. CONCLUSIONS: Our study paves the way for investigating the clinical determinants of graphomotor tilts, including impaired verticality perception, to better understand their underlying mechanisms.

Tissue-specific expression and drought responsiveness of cell-wall invertase genes of rice at flowering.

Drought stress near heading reduces grain yield in rice cultivars by inhibiting processes such as anther dehiscence and panicle exsertion. Because cell-wall invertases play an important role in carbon allocation to developing organs, we examined the tissue-specific expression and drought sensitivity of the corresponding genes (OsCIN1-9) at heading in the widely grown cultivar IR64. OsCIN1-5,8 were expressed to varying degrees in flag leaf, panicle, anthers and peduncle at 1 day before heading (1 DBH). When water was withheld for 2 days starting 3 DBH, anthesis and peduncle elongation were halted. At the same time, transcript levels for OsCIN1-5,8 genes were all markedly down-regulated in anthers and/or peduncles but were not affected in flag leaves. Re-watering allowed anthesis and peduncle elongation to proceed and restored expression of OsCIN1-5,8. We conclude that cell-wall invertase genes, as a class, respond rapidly to water deficit in anthers and peduncles and through a reduction in sink strength help to coordinate a delay in anthesis and heading. By contrast, vacuolar invertase OsVIN2 was up-regulated by drought stress in flag leaves, panicles, anthers and peduncles. Although OsCIN1-3,5,8 were active in the peduncle, only OsCIN2 was expressed strongly and preferentially at the base, where cell division and cell elongation occur. OsCIN2 was expressed principally in the primary and secondary vascular systems, consistent with a role in diverting sucrose from the phloem to the dividing and expanding cells of the peduncle, whereas the less abundant OsCIN1,3,5,8 transcripts were found principally in parenchyma cells. The OsCIN2 transcript levels in the base were highest at 1 DBH, when rapid peduncle elongation began. Drought stress halted peduncle elongation and reduced OsCIN2 transcript level to 8% of the control level. On re-watering, peduncle elongation was restored and OsCIN2 transcript level recovered to 24% of the control. The abscisic acid (ABA) level of peduncles increased 7-fold on drought stress and returned to the control level on re-watering. Detached peduncles floated on water elongated little and lost all OsCIN2 transcripts, but on 50-100 microM GA3 they elongated rapidly and maintained high OsCIN2 transcript levels. ABA antagonized both peduncle elongation and maintenance of OsCIN2 transcript levels. We conclude that this antagonism is a potential intervention point for breeding strategies directed at enhancing panicle exsertion during or after drought stress at heading.

Hydraulic conductivity of rice roots.

A pressure chamber and a root pressure probe technique have been used to measure hydraulic conductivities of rice roots (root Lp(r) per m(2) of root surface area). Young plants of two rice (Oryza sativa L.) varieties (an upland variety, cv. Azucena and a lowland variety, cv. IR64) were grown for 31-40 d in 12 h days with 500 micromol m(-2) s(-1) PAR and day/night temperatures of 27 degrees C and 22 degrees C. Root Lp(r) was measured under conditions of steady-state and transient water flow. Different growth conditions (hydroponic and aeroponic culture) did not cause visible differences in root anatomy in either variety. Values of root Lp(r) obtained from hydraulic (hydrostatic) and osmotic water flow were of the order of 10(-8) m s(-1) MPa(-1) and were similar when using the different techniques. In comparison with other herbaceous species, rice roots tended to have a higher hydraulic resistance of the roots per unit root surface area. The data suggest that the low overall hydraulic conductivity of rice roots is caused by the existence of apoplastic barriers in the outer root parts (exodermis and sclerenchymatous (fibre) tissue) and by a strongly developed endodermis rather than by the existence of aerenchyma. According to the composite transport model of the root, the ability to adapt to higher transpirational demands from the shoot should be limited for rice because there were minimal changes in root Lp(r) depending on whether hydrostatic or osmotic forces were acting. It is concluded that this may be one of the reasons why rice suffers from water shortage in the shoot even in flooded fields.

Mapping osmotic adjustment in an advanced back-cross inbred population of rice.

Osmotic adjustment is one of several characters putatively associated with drought tolerance in rice. Indica cultivars are known to have a greater capacity for osmotic adjustment than japonica cultivars. We developed an advanced back-cross population using an indica donor, IR62266-42-6-2, to introgress osmotic adjustment into an elite japonica cultivar, IR60080-46A. One hundred and fifty BC(3)F(3) families were genotyped using microsatellites and RFLP markers, and a few candidate genes. We evaluated osmotic adjustment in these lines under greenhouse conditions using the re-hydration technique. Using the composite interval mapping technique, we detected 14 QTLs located on chromosomes 1, 2, 3, 4, 5, 7, 8 and 10 that together explained 58% of the phenotypic variability. Most, but not all, of the alleles with positive effects came from the donor parent. On chromosome 8, two QTLs were associated in repulsion. The QTL locations were in good agreement with previous studies on this trait on rice and in other cereals. Some BC(3)F(3) lines carried the favorable alleles at the two markers flanking up to four QTLs. Intercrossing these lines followed by marker-aided selection in their progenies will be necessary to recover lines with levels of osmotic adjustment equal to the donor parent. The advanced back-cross strategy appeared to be an appropriate method to accelerate the process of introgressing interesting traits into elite material.