Investigation of heterochronic bolting in lettuce.

Abstract

The premature loss of rosette habit also called “heterochronic bolting” is an undesired trait in lettuce cultivars. As part of the LettuceKnow programme, this research project focuses on the rosette habit of the lettuce accessions LK08, LK27, LK40, LK43, LK44 and LK46 by the analysis of elongation of internodes under two different temperature conditions (22°C and 27°C LD) from 12 to 22 days after germination. The six analysed accessions show clear differences in their extent of internode elongation between accessions, with similar trends of first, average and total internode lengths. The elongation behaviour seems to resemble the previously mapped bolting behaviour for 22°C LD conditions, while some deviations are visible in 27°C growth conditions. To gain insights into the role of the genes Arabidopsis thaliana homeobox gene 1 (ATH1), phytochrome interacting factor 3 (PIF3) and phytochrome interacting factor 7 (PIF7) on early internode elongation (heterochronic bolting), quantitative RT-PCR (qPCR) is performed on meristem enriched tissue of the accessions LK27, LK40, LK43 and LK44 at 22°C and 27°C conditions, with the focus of the analysis lying on ATH1 and PIF7. Results show significant differences in the expression of PIF7 between Day 5 and Day 12 for the accessions LK40 and LK44, with a similar trend evident for LK27 and LK43. For future investigation of mutant plants, a CRISPR-Cas9 knock-out construct of LsPIF7 was created using golden gate cloning and successfully transformed into LK27.