Question

Genes located in the chloroplast genome can be spliced to generate mature transcripts. However, unlike splicing in the nucleus, exons of chloroplast genes can be transcribed separately and trans-spliced to generate the mature transcripts. The psbD mRNA is co-transcribed with exon 2 of the psaA transcript. In the nac2-26 mutant the psaA transcript accumulates normally suggesting that either the splicing of psaA happens faster than the degradation of psbD OR that the NAC2 protein is required to stabilize psbD only after splicing. Which of the above possibilities is the answer and how did the authors distinguish between these possibilities? What would the data have looked like if the opposite possibility were true?

Answer 1

The accumulation of the psaA transcript suggests that the NAC2 protein is essential for the stabilization of the psbD only after the splicing. The mutant of NAC2 causing the accumulation of the psaA lead to an unstable DNA, which points to the possibility that the NAC2 protein must be required for the stabilizing of the psbD gene. The instability of the psbD causes the rapid degradation of the RNA.

If the other situation would have been true then it would have lead to the delayed expression of the psbD gene, and the degradation of the RNA would not have taken place.