Os01g0898300

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Annotated Information

Function

OsSPR1 was identified by map-based cloning. It encodes a novel mitochondrial protein with the Armadillo-like repeat domain. Osspr1 mutants exhibited decreased root cell elongation. The large reduction of Fe content observed in the leaves but not the roots of Osspr1 mutant plants under Fe(II) and Fe(III) nutrient supply, and the normal Fe deficiency response for both strategy I and II marker genes in the leaves but not the roots indicate a defect in Fe homeostasis. In addition, root development was also compromised in Osspr1 mutant plants. It is likely that the defective roots of Osspr1 plants will have a secondary effect on nutrient uptake. However, if reduced Fe uptake as a result of damaged roots was the primary reason for the reduced Fe content in the leaves, the Fe content and the Fe deficiency response would have been duced and activated, respectively, in the roots. However, the Fe content in roots of Osspr1 mutant plants was similar to that of wild-type plants (Fig. 6e). Also, no Fe deficiency response was observed in roots (Fig. 7). However, a lower Fe content was observed in the mutant leaves, which was inconsistent with the induction of Fe-responsive genes (Figs 6c, 7). These results indicate that OsSPR1 plays a role in maintaining Fe (and other metal) homeostasis between roots and leaves.

Expression

The expression pattern of OsSPR1 was determined usingt he GUS gene driven by the OsSPR1 promoter transferred into wild-type plants. GUS staining in transgenic plants indicated that OsSPR1 was ubiquitously expressed in all plant organs, including the root, leaf, stem and spikelet (Fig. 3a–r). OsSPR1 was expressed in primary and lateral roots, both in mature regions and in root tips. Strong expression was observed in the root tip (in the meristem and lateral root initiation regions), where dividing cells are present. The expression of OsSPR1 in the root is mainly associated with vascular tissues (Fig. 3b,d,h). Semiquantitative RT-PCR analysis using SPR1-specific primers showed that SPR1 was expressed at relatively similar levelsin all tissues, including the root, stem base, stem, leaf and panicles (Fig. 3s), consistent with the GUS staining patterns observed.

Evolution

Root elongation is determined by two successive processes: cell elongation and cell proliferation (Beemster et al., 2003). In rice, several genes controlling division and differentiation in root growth and development have been identified through genetic screens (Rebouillat et al., 2009). Here, we cloned OsSPR1, a novel mitochondrial gene involved in root cell elongation. Loss of function of OsSPR1 resulted in defective root elongation, including primary root, adventitious root and lateral root elongation; notably, the defects were more severe in lateral roots and adventitious roots. Analysis of the different root zones revealed similar arrangements of cells in those zones compared with the wild type, but reduced cell length was observed in the spr1 roots, suggesting that reduced root length in spr1 resulted from reduced cell elongation.

Labs working on this gene

• Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology (VIB), Ghent University, Belgium.
• State Key Laboratory of Plant Physiology and Biochemistry, College of Life Science, Zhejiang University, Hangzhou 310058, China
• ARC Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, 6009 WA, Australia
• Joint Laboratory in Genomics and Nutriomics, College of Life Science, Zhejiang University, Hangzhou 310058, China
• Institute of Virology and Biotechnology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China

References

1.Beemster GTS, Fiorani F, Inze´ D. 2003. Cell cycle: the key to plant growth control? Trends in Plant Science 8: 154–158.

2.Rebouillat J, Dievart A, Verdeil J, Escoute J, Giese G, Breitler J, Gantet P, Espeout S, Guiderdoni E, Pe´rin C. 2009. Molecular genetics of rice root development. Rice 2: 15–34.

3.Liqiang Jia;Zhongchang Wu;Xi Hao;Chris Carrie;Libin Zheng;James Whelan;Yunrong Wu;Shoufeng Wang;Ping Wu;Chuanzao Mao. Identification of a novel mitochondrial protein, short postembryonic roots 1 (SPR1), involved in root development and iron homeostasis in Oryza sativa.New Phytologist, 2011, 189(3): 843-855.

4.Jia LiQiang . Is Reactive Oxygen Species (ROS) the underlying factor for inhibited root growth in Osspr1? Plant Signaling & Behavior, 2011, 6(7): 1024-1025.