Cytological evidence of BSD2 functioning in both chloroplast division and dimorphic chloroplast formation in maize leaves

Heying Li,Xingshan Jiang,Rongxin Shen,Hong Wu,Huina Wang,Mei Bai,Haiyang Wang

doi:10.1186/s12870-019-2219-7

Heying Li, Xingshan Jiang + Show 5 more

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https://doi.org/10.1186/s12870-019-2219-7

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Journal: BMC Plant Biology	Publication Date: Jan 9, 2020
Citations: 5	License type: open-access

Affiliation: South China Agricultural University

Abstract

BackgroundMaize 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.ResultsWe 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.ConclusionsOur 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.

Highlights

Maize bsd2 is a classical C4 mutant with defective C4 photosynthesis, accompanied with reduced accumulation of Rubisco and aberrant mature chloroplast morphology in the bundle sheath (BS) cells
Mutation of BSD2 Disturbs chloroplast grana stacking and starch accumulation To investigate the roles of BSD2 in the regulation of leaf development, we examined the leaf anatomy in twelveday old bsd2 mutant and wild type plants (Fig. 1a)
Light micrograph observation showed that the M and BS cells of the Kranz anatomy were well developed in leaves of both wild type and the bsd2 mutant (Fig. 1b)

Summary

Introduction

Maize bsd (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. 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. Li et al BMC Plant Biology (2020) 20:17 development of Kranz anatomy is regulated, which is essential for the genetic engineering of C3 crop species (such as rice) with C4 photosynthesis characteristics [9,10,11]. OAA is metabolized into malate and diffused into the BS cells in order to increase CO2 concentration around Rubisco. This particular mechanism enhances the carboxylation reaction of Rubisco, which significantly increased the photosynthetic yield [15, 16]

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