BACKGROUND Maize bsd2 (bundle sheath defective2) is a classical C4 mutant with defective C4 photosynthesis, accompanied with reduced accumulation of Rubisco (ribulose bisphosphate carboxylase oxygenase) and aberrant mature chloroplast morphology in the bundle sheath (BS) cells. However, as a hypothetical chloroplast chaperone, the effects of BSD2 on C4 chloroplast development have not been fully examined yet, which precludes a full appreciation of BSD2 function in C4 photosynthesis. The aims of our study are to find out the role ofBSD2 in regulating chloroplasts development in maize leaves, and to add new insights into our understanding of C4 biology. RESULTS We found that at the chloroplast maturation stage, the thylakoid membranes of chloroplasts in the BS and mesophyll (M) cells became significantly looser, and the granaof chloroplasts in the M cells became thinner stacking in the bsd2 mutant when compared with the wildtype plant. Moreover, at the early chloroplast development stage, the number of dividing chloroplasts and the chloroplast division rate are both reduced in the bsd2 mutant, compared with wild type. Quantitative reverse transcriptase-PCR analysis revealed that the expression of both thylakoid formation-related genesand chloroplast division-related genes is significantly reduced in the bsd2 mutants. Further, we showed that BSD2 interacts physically with the large submit of Rubisco (LS) in Bimolecular Fluorescence Complementation assay. CONCLUSIONS Our combined results suggest that BSD2 plays an essential role in regulating the division and differentiation of the dimorphic BS and M chloroplasts, and that it acts at a post-transcriptional level to regulate LS stability or assembly of Rubisco.

中文翻译：

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BSD2在玉米叶片的叶绿体分裂和双态叶绿体形成中起作用的细胞学证据。

背景玉米bsd2（束鞘缺陷2）是具有缺陷的C4光合作用的经典C4突变体，伴随着束鞘（核糖二磷酸羧化酶加氧酶）的积累减少和束鞘（BS）细胞中异常成熟的叶绿体形态。然而，作为假设的叶绿体伴侣，尚未完全检查BSD2对C4叶绿体发育的影响，因此无法完全了解BSD2在C4光合作用中的功能。我们的研究目的是找出BSD2在调节玉米叶中叶绿体发育中的作用，并为我们对C4生物学的理解增添新见解。结果我们发现，在叶绿体成熟阶段，BS和叶肉（M）细胞中叶绿体的类囊体膜明显变松，与野生型植物相比，bsd2突变体中M细胞中叶绿体的堆积变薄。而且，在bsd2突变体中，与野生型相比，在早期叶绿体发育阶段，叶绿体的分裂数和叶绿体的分裂率均降低。定量逆转录PCR分析表明，在bsd2突变体中，类囊体形成相关基因和叶绿体分裂相关基因的表达均显着降低。此外，我们在双分子荧光互补测定中显示BSD2与Rubisco（LS）的大量提交物发生物理相互作用。结论我们的综合结果表明BSD2在调节双态BS和M叶绿体的分裂和分化中起着至关重要的作用，