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Key Message: Current development of advanced biotechnology tools allows us to characterize the role of key genes in plant productivity. The implementation of this knowledge in breeding strategies might accelerate the progress in obtaining high-yielding cultivars. The achievements of the Green Revolution were based on a specific plant ideotype, determined by a single gene involved in gibberellin signaling or metabolism. Compared with the 1950s, an enormous increase in our knowledge about the biological basis of plant productivity has opened new avenues for novel breeding strategies. The large and complex genomes of diploid barley and hexaploid wheat represent a great challenge, but they also offer a large reservoir of genes that can be targeted for breeding. We summarize examples of productivity-related genes/mutants in wheat and barley, identified or characterized by means of modern biology. The genes are classified functionally into several groups, including the following: (1) transcription factors, regulating spike development, which mainly affect grain number; (2) genes involved in metabolism or signaling of growth regulators-cytokinins, gibberellins, and brassinosteroids-which control plant architecture and in consequence stem hardiness and grain yield; (3) genes determining cell division and proliferation mainly impacting grain size; (4) floral regulators influencing inflorescence architecture and in consequence seed number; and (5) genes involved in carbohydrate metabolism having an impact on plant architecture and grain yield. The implementation of selected genes in breeding programs is discussed, considering specific genotypes, agronomic and climate conditions, and taking into account that many of the genes are members of multigene families.

Cold stress responses in plants are highly sophisticated events that alter the biochemical composition of cells for protection from damage caused by low temperatures. In addition, cold stress has a profound impact on plant morphologies, causing growth repression and reduced yields. Complex signalling cascades are utilised to induce changes in cold-responsive gene expression that enable plants to withstand chilling or even freezing temperatures. These cascades are governed by the activity of plant hormones, and recent research has provided a better understanding of how cold stress responses are integrated with developmental pathways that modulate growth and initiate other events that increase cold tolerance. Information on the hormonal control of cold stress signalling is summarised to highlight the significant progress that has been made and indicate gaps that still exist in our understanding.

Key Message: By comparing series full-length cDNA libraries stressed and control, the dynamic process of salt stress response in Upland cotton was studied, and reactive oxygen species and gibberellins signaling pathways were proposed. The Upland cotton is the most important fiber plant with highly salt tolerance. However, the molecular mechanism underlying salt tolerance in domesticated cotton was unclear. Here, seven full-length cDNA libraries were constructed for seedling roots of Upland cotton 'Zhong G 5' at 0, 3, 12 and 48 h after the treatment of control or 150 mM NaCl stress. About 3300 colonies in each library were selected robotically for 5'-end pyrosequencing, resulting in 20,358 expressed sequence tags (ESTs) totally. And 8516 uniESTs were then assembled, including 2914 contigs and 5602 singletons, and explored for Gene Ontology (GO) function. GO comparison between serial stress libraries and control reflected the growth regulation, stimulus response, signal transduction and biology regulation processes were conducted dynamically in response to salt stress. MYB, MYB-related, WRKY, bHLH, GRAS and ERF families of transcription factors were significantly enriched in the early response. 65 differentially expressed genes (DEGs), mainly associated with reactive oxygen species (ROS) scavenging, gibberellins (GAs) metabolism, signal transduction, transcription regulation, stress response and transmembrane transport, were identified and confirmed by quantitative real-time PCR. Overexpression of selected DEGs increased tolerance against salt stress in transgenic yeast. Results in this study supported that a ROS-GAs interacting signaling pathway of salt stress response was activated in Upland cotton. Our results provided valuable gene resources for further investigation of the molecular mechanism of salinity tolerance.

Panicle exsertion, an essential physiological process for obtaining high grain yield in rice is mainly driven by peduncle (uppermost internode) elongation. Drought at heading/panicle emergence prevented peduncle elongation from reaching its maximum length even after re-watering. This inhibitory effect of drought resulted in delayed heading and trapping spikelets lower down the panicle inside the flag-leaf sheath, thus increasing sterility in the lower un-exserted spikelets and also among the upper superior spikelets whose exsertion was delayed. Intermittent drought stress caused a significant reduction in relative water content (RWC) and an increase in the abscisic acid (ABA) level of the peduncles, while both returned to normal levels upon re-watering. Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis revealed the down-regulation of GA biosynthetic genes during drought. 2D-PAGE analysis of proteins from peduncles collected under well-watered, drought-stressed, and re-watered plants revealed at least twofold differential changes in expression of 31 proteins in response to drought and most of these changes were largely reversed by re-watering. The results indicate that ABA-GA antagonism is a key focal point for understanding the failure of panicle exsertion under drought stress and the consequent increase in spikelet sterility.

A higher concentration of H2O2 was detected in the sense transgenic potato plant (SS4) with the lily chCu,ZnSOD sequence, whereas higher levels of O2(-) was detected in the antisense transgenic plant (SA1) than the WT plant. The elongation growth in SA1 was significantly inhibited by treatment with diphenyleneiodonium, an inhibitor of O2(-) generation, and promoted in the SS4 on treatment with herbicide methyl viologen, a generator of apoplastic O2(-) . Higher concentrations of GAs were detected during plant growth and the early stage of tuberization in SA1. Complete recovery of the above elongation growth and microtuberization pattern in transgenic plants following treatment of GA(3) or an inhibitor of gibberellin synthesis, paclobutrazol, indicate that these changes were mainly caused by active GA levels. In conclusion, a specific ROS (O2(-) ) acts as a signal transducer via GA biosynthetic pathways for the regulation of plant growth and tuber development of potato.

We have isolated a severe dwarf transposon (Ds) insertion mutant in rice (Oryza sativa L.), which could be differentiated early in the seedling stage by reduced shoot growth and dark green leaves, and later by severe dwarfism and failure to initiate flowering. These mutants, however, showed normal seed germination and root growth. One of the sequences flanking Ds, rescued from the mutant, was of a chromosome 4-located putative ent-kaurene synthase (KS) gene, encoding the enzyme catalyzing the second step of the gibberellin (GA) biosynthesis pathway. Dwarf mutants were always homozygous for this Ds insertion and no normal plants homozygous for this mutation were recovered in the segregating progeny, indicating that the Ds insertion mutation is recessive. As mutations in three recently reported rice GA-responsive dwarf mutant alleles and the dwarf mutation identified in this study mapped to the same locus, we designate the corresponding gene OsKS1. The osks1 mutant seedlings were responsive to exogenous gibberellin (GA3). OsKS1 transcripts of about 2.3 kb were detected in leaves and stem of wild-type plants, but not in germinating seeds or roots, suggesting that OsKS1 is not involved in germination or root growth. There are at least five OsKS1-like genes in the rice genome, four of which are also represented in rice expressed sequence tag (EST) databases. All OsKS1-like genes are transcribed with different expression patterns. ESTs corresponding to all six OsKS genes are represented in other cereal databases including barley, wheat and maize, suggesting that they are biologically active.

Dwarf plants are useful in research because multiple plants can be grown in a small area. Rice (Oryza sativa L.) is especially important since its relatively simple genome has recently been sequenced. We are characterizing a gibberellic acid (GA) mutant of rice (japonica cv 'Shiokari,' line N-71) that is extremely dwarf (20 cm tall). Unfortunately, this GA mutation is associated with poor germination (70%) under aerobic conditions. Neither exogenous GA nor a dormancy-breaking heat treatment improved germination. However, 95% germination was achieved by germinating the seeds anaerobically, either in a pure N2 environment or submerged in unstirred tap water. The anaerobic conditions appear to break a mild post-harvest dormancy in this rice cultivar., (Copyright 2002 Crop Science Society of America.)