Functional Study And Application Of Rice OsPDCD5 Gene And Functional Identification Of Rape CsRRM2 Domain In Cotton

Programmed cell death (PCD) has been defined as a sequence of events that lead to the controlled and organized destruction of a cell. This process is crucial for organismal defense responses, to restrict the spread of pathogens, and for proper development of a multicellular body plan.OsPDCD5 is a homolog gene of PDCD5, which is involved in PCD regulation and conserved in the course of evolution. In our previous research, constitutive overexpression of OsPDCD5 proved to induce plant death in rice, but none of the regenerated transgenic plant died until 3-leaf stage.Why OsPDCD5did not effect in younger plants? Is there not enough amount of OsPDCD5transcripts until 3-leaf stageor there are some mechanisms which prevent OsPDCD5 function in younger plants? To resolve this problem, a system of inducible OsPDCD5 expression is required. Heat shock proteins (HSPs) have been detected during thermal stress in all organisms examined, ranging from bacteria to human beings. The heat inducible expression of HSPs results from the heat inducible transcription of HSP gene promoters. Oshsp 16.9C(Accession No. U81385) is a kind of rice class I low-molecular-mass HSP gene that is barely transcribed at 28?, but the concentration of Oshsp 16.9C mRNA increases significantly in rice heat-shocked at 41?for 2 h. In this work,Oshsp 16.9C promoter-driven OsPDCD5was used for the transformation of japonica rice Zhonghua 11 and indica rice 9311. The resulting transgenic plants grew normally at 28?and OsPDCD5 transcription could be induced at any developmental stage by heat shockat 41?, which allowed detailed, systematic study of OsPDCD5 induced rice cell death.The results showed that in 3-leaf stage and older seedlings, ectopic OsPDCD5 expression could independently induce cell death. In altered plants, OsPDCD5 expression caused a lesion mimic phenotype, abnormal leaf morphology, DNA fragmentation, H2O2 production, and mitochondrial distortion. Transcript microarray analysis revealed that many PCD-related genes were involved, including Bcl-2-associated athanogene (BAG) family genes and a homolog gene of AtBAG6, which can induce PCD in yeast and the Arabidopsis plant. Nevertheless, ectopic OsPDCD5 expression failed to induce any visibly morphological phenotype in 2-leaf stage and younger seedlings. At the same time, transcript microarray analysis and quantitative RT-PCR showed the mRNA level of a Bax inhibitor-1 gene and an ubiquitin gene changed, suggesting young seedlings possess some mechanisms which inhibit this OsPDCD5-induced cell death. These findings strongly suggest that the OsPDCD5 gene critically regulates the execution of PCD and calcium induced mitochondrial dysfunction may play an important role in this pathway.The antisense-OsPDCD5 transgenic J23B plants demonstrate a delay of heading date and leaf senescence, leading to a great increase on grain yield. Furthermore,the OsPDCD5 inducible expression system can be used to regenerate marker-free transgenic plants by co-transformation, indicating OsPDCD5is of great practical application value.Cotton (Gossypium hirsutum L.) is the dominant source of natural textile fiber and a significant oil crop and has been a valued agricultural commodity for more than 8000 years. Many cotton improvement programs have been established to improve this crop. The key goals are to improve the yield and the quality of the fiber. The appropriate botanically term for cotton fiber is trichome, which is developed from the ovule epidermis and is not part of the vascular tissue. While the majority of plant trichomes are multicellular, cotton trichome cells are unicellular. As cotton fiber cell is highly elongated, its length basically represents its size. Cotton fiber length affects yarn strength, yarn evenness, and spinning efficiency. Thus, thelengthof cotton trichome cell not only affects yield but also cotton quality. The average length of unicellular cotton fibers varies with genotype and is apparently under homeostatic control. However, not much is known about the underlying aspect of the control. Thus, information that can shed light on the control could be useful for improving cotton fiber yield and quality.We have previously found that cell size and yield of rice (Oryza sativa) can be increased by overexpression of RNA recognition motif (RRM) FCA-RRM1, as well as FCA-RRM2, of the rice flowering control gene FCA (6,7). This suggests that FCA-RRM1 and FCA-RRM2 both play a role in homeostatic cell size regulation. Both FCA-RRMs exhibit a high degree of evolutionary conservation in plant. The high degree of homology suggests that this RRM domain might have similar function in different plants. Indeed, we observed that overexpression of Brassica napusFCA-RRM2 (Bn-csRRM2) also increased the cell size of B. napus (unpublished data).In order to validate the inter-species effect of Bn-csRRM2 function, cotton (Gossypium hirsutum) was used for transformation. The results showed that Bn-csRRM2 even worked in cotton, suggesting csRRM2 might be an ancient and common cell size regulator.Although the mechanism by which csRRM2 influences cell size regulation is still unclear, csRRM2 offers a potential way to resolve this problem. Besides its biological significance, csRRM2 also has great economic value and considerable influence on cotton industry because it leads to visible increase on both fiber quality and fiber yield which are exceedingly difficult to incorporate into a single breeding program. Thinking of the high conservation of csRRM2, it may also work in other crops, such as Triticum aestivum, Populus trichocarpa and Ricinus communis.