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OsPDCD5 is the rice ( Oryza sativa L.) homolog of PDCD5, a gene involved in programmed cell death (PCD) regulation and highly conserved over time. PDCD5 overexpression in tumor cells enhances apoptosis triggered by growth factor or serum deprivation. In our previous research, constitutive OsPDCD5 overexpression induces early death in transgenic plants. In this study, an inducible OsPDCD5 expression strategy was employed to systematically study the role of OsPDCD5 in rice. With this system, OsPDCD5 was found to be capable of independently inducing cell death in three-leaf stage and older seedlings. These altered plants exhibited lesion mimic phenotype, abnormal leaf morphology, DNA fragmentation, hydrogen peroxide production, and mitochondrial distortion. In nature, RNA hybridization in situ has shown that OsPDCD5 expression was predominantly localized to the tapetal layer where PCD occurred. Transcript microarray analyses here revealed that many PCD-related genes were involved. These data, taken together, indicated that OsPDCD5-induced cell death is a kind of PCD. Nevertheless, OsPDCD5 failed to induce any visible morphological phenotypes in two-leaf stage and younger seedlings. Transcript microarray analyses and quantitative real-time polymerase chain reaction showed that the Bax inhibitor-1 (BI-1) mRNA concentration and the activity of an ubiquitin gene were specifically changed. Endogenous OsPDCD5 upregulation, induced by ectopic OsPDCD5 expression in three-leaf stage seedlings, was also absent in two-leaf stage seedlings, suggesting strongly that young seedlings could inhibit PCD at some level. [ABSTRACT FROM AUTHOR]

A dwarf mutant, designated LB4D, was obtained among the progeny of backcrosses to a wild rice introgression line. Genetic analysis of LB4D indicated that the dwarf phenotype was controlled by a single semidominant dwarfing gene, which was named LB4D. The mutants were categorized as dn‐type dwarf mutants according to the pattern of internode reduction. In addition, gibberellin (GA) response tests showed that LB4D plants were neither deficient nor insensitive to GA. This study found that tiller formation by LB4D plants was decreased by 40% compared with the wild type, in contrast to other dominant dwarf mutants that have been identified, indicating that a different dwarfing mechanism might be involved in the LB4D dominant mutant. The reduction of plant height in F1 plants ranged from 27.9% to 38.1% in different genetic backgrounds, showing that LB4D exerted a stronger dominant dwarfing effect. Using large F2 and F3 populations derived from a cross between heterozygous LB4D and the japonica cultivar Nipponbare, the LB4D gene was localized to a 46 kb region between the markers Indel 4 and Indel G on the short arm of chromosome 11, and four predicted genes were identified as candidates in the target region. [ABSTRACT FROM AUTHOR]