Changes in plastid biogenesis leading to the formation of albino regenerants in barley microspore culture

Abstract

Background Microspore embryogenesis is potentially the most effective method of obtaining doubled haploids (DH) which are utilized in breeding programs to accelerate production of new cultivars. However, the regeneration of albino plants significantly limits the exploitation of androgenesis for DH production in cereals. Despite many efforts, the precise mechanisms leading to development of albino regenerants have not yet been elucidated. The objective of this study was to reveal the genotype-dependent molecular differences in chloroplast differentiation that lead to the formation of green and albino regenerants in microspore culture of barley. Results We performed a detailed analysis of plastid differentiation at successive stages of androgenesis in two barley cultivars, ‘Jersey’ and ‘Mercada’ that differed in their ability to produce green regenerants. We demonstrated the lack of transition from the NEP-dependent to PEP-dependent transcription in plastids of cv. ‘Mercada’ that produced mostly albino regenerants in microspore culture. The failed NEP-to-PEP transition was associated with the lack of activity of Sig2 gene encoding a sigma factor necessary for transcription of plastid rRNA genes. A very low level of 16S and 23S rRNA transcripts and impaired plastid translation machinery resulted in the inhibition of photomorphogenesis in regenerating embryos and albino regenerants. Furthermore, the plastids present in differentiating ‘Mercada’ embryos contained a low number of plastome copies whose replication was not always completed. Contrary to ‘Mercada’, cv. ‘Jersey’ that produced 90% green regenerants, showed the high activity of PEP polymerase, the highly increased expression of Sig2, plastid rRNAs and tRNAGlu, which indicated the NEP inhibition. The increased expression of GLKs genes encoding transcription factors required for induction of photomorphogenesis was also observed in ‘Jersey’ regenerants. Conclusions Proplastids present in microspore-derived embryos of albino-producing genotypes did not pass the early checkpoints of their development that are required for induction of further light-dependent differentiation of chloroplasts. The failed activation of plastid-encoded RNA polymerase during differentiation of embryos was associated with the genotype-dependent inability to regenerate green plants in barley microspore culture. The better understanding of molecular mechanisms underlying formation of albino regenerants may be helpful in overcoming the problem of albinism in cereal androgenesis.

Plasmotype condition nuclear pleiotropic effects on clock and fitness in barley

“…In the current diallel, the rpoC1 and matK (position: 2099) co-segregate and this matK/rpoC1 haplotype is significantly associated with DTF under AT and HT (P <0.0001) but not with the clock traits. However, another member of the PEP complex (Hess et al, 1993; Gajecka et al, 2021), i.e. rpoC2 , appeared as a significant QTLs for several growth and reproductive traits.…”

The Effect of Daminozide, Dark/Light Schedule and Copper Sulphate in Tissue Culture of Triticum timopheevii

“…The impact of genotype on the occurrence of albino plants is more prominent in androgenic cultures of cereals. Albinism in anther cereal cultures was accompanied by various changes that take place in the chloroplast genome, such as the micro-and macro-deletion of photosynthetic and structural plastid-localized genes [58,59] and changes in their copy number [19]. On the other hand, the appearance of the albino phenotype is also controlled by various nuclear-localized genes, without changes in the plastid genome [60].…”

“…In barley, it was found that the ability of genotypes to regenerate green plants in androgenic cultures depends on the level of differentiation of microspore plastids in vivo [19]. It has been suggested that the molecular changes leading to the albino phenotype are genetically determined before the introduction of microspores into the in vitro culture [64].…”

“…The precise mechanism underlying chlorophyll deficiency in regenerated plants has not yet been elucidated. It is associated with impaired chloroplast biogenesis and the inability of proplastids to differentiate into functional chloroplasts during the various phases of somatic embryo formation and development [19]. Since the process of chlorophyll biosynthesis requires a complex of elements and compounds, various approaches have been used to overcome albinism in tissue cultures with varying degrees of success.…”

Understanding In Vitro Tissue Culture-Induced Variation Phenomenon in Microspore System

“…The expression of granule-bound starch synthase I ( GBSSI ) gene in early-mid microspores correlated with a genotype ability to regenerate green plants via androgenesis [ 194 ]. Results concerning the role of nuclear and plastic-encoded polymerases in albino and green plant regeneration indicating antero- and retrograde phenomenon in barley were presented from the same group [ 195 ]. Research conducted on Arabidopsis thaliana has shown that the transcriptome composition changes significantly during callus induction in plant tissue culture, proving the high dynamics of DNA methylation [ 196 ].…”