Chloroplast genes are transcribed by the plastid-encoded RNA polymerase
(PEP) or nucleus$B!>(Bencoded RNA polymerase. FRUCTOKINASE$B!>(BLIKE PROTEINS (FLNs)
are carbohydrate kinases that act as part of the PEP complex. However, the
mechanisms underlying FLN activity are quite unknown. In their study, the
team of Lei He of the China National Rice Research Institute studied the
OsFLN1 gene, a homolog of HSA1/OsFLN2, and the effect of its knockout on
chloroplast biogenesis.

The team found that OsFLN1 is localized in the chloroplast. Analysis
revealed that OsFLN1 and HSA1/OsFLN2 interact with THIOREDOXINZ (OsTRXz) to
regulate chloroplast development. To prove this, the team generated fln1
knockout mutants via CRISPR-Cas9. These mutants exhibited severe albino
phenotype and seedling lethality. The team also developed OsTRXz-knockout
mutants, which also showed a similar albino and seedling lethality phenotype
to that of the fln1 mutants.

Further analysis revealed that the transcription and translation of PEP$B!>(B
dependent genes were strongly inhibited in fln1 and trxz mutants.

These results show that OsFLN1 and HSA1/OsFLN2 contribute to chloroplast
biogenesis and plant growth.



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