Abstract
The proliferation and development of chloroplasts are important for maintaining the normal chloroplast population in plant tissues. Most studies have focused on chloroplast maintenance in leaves. In this study, we identified a spontaneous mutation in a tomato mutant named suffulta (su), in which the stems appeared albinic while the leaves remained normal. Map-based cloning showed that Su encodes a DnaJ heat shock protein that is a homolog of the Arabidopsis gene AtARC6, which is involved in chloroplast division. Knockdown and knockout of SlARC6 in wild-type tomato inhibit chloroplast division, indicating the conserved function of SlARC6. In su mutants, most mesophyll cells contain only one or two giant chloroplasts, while no chloroplasts are visible in 60% of stem cells, resulting in the albinic phenotype. Compared with mature tissues, the meristem of su mutants suggested that chloroplasts could partially divide in meristematic cells, suggesting the existence of an alternative mechanism in those dividing cells. Interestingly, the adaxial petiole cells of su mutants contain more chloroplasts than the abaxial cells. In addition, prolonged lighting can partially rescue the albinic phenotypes in su mutants, implying that light may promote SlACR6-independent chloroplast development. Our results verify the role of SlACR6 in chloroplast division in tomato and uncover the tissue-specific regulation of chloroplast development.
Highlights
Chloroplasts are an important organelle where plants absorb solar energy and produce sugars[1]
Our results showed that the levels of multiple chlorophylls, including Chla, Chlb, Car, and total Chl, in su stems were significantly lower than those in wild type (WT) stems, but such a difference was not detected in the leaves (Fig. 1M, N)
The pale color and the defective chlorophyll content prompted us to hypothesize that the albinic phenotype in su mutants might derive from the absence of chlorophyll precursors or dysfunctional chloroplasts
Summary
Chloroplasts are an important organelle where plants absorb solar energy and produce sugars[1]. In Arabidopsis, a number of mutants that are defective in the accumulation and replication of chloroplasts (arc) have been identified, in which chloroplast number, size, and shape are severely affected[2,3,4,5]. Similar to their original microbial ancestors, chloroplasts replicate by binary fission in plants, which is driven by ring-like dynamic division machinery located at the middle of the organelle[6,7,8,9]. The contractile component of the division machinery is composed of the
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