The promoters of 3 celery salt-induced phloem-specific genes as new tools for monitoring salt stress responses

Genes induced by a progressive 3 week salt stress (final NaCl concentration 300 mM) were identified in the phloem of celery (Apium graveolens L., cv Vert d’Elne). A subtractive library was constructed and screened for salt-induced, phloem-specific genes. Work was focused on phloem due to its central role in inter-organ exchanges. Three genes were studied in more details, 2 coding for metallothioneins (AgMT2 and AgMT3) and one for a new mannitol transporter (AgMaT3). Expression of a reporter gene in transgenic Arabidopsis under control of promoter of each gene was located in the phloem. pAgMT2 has a typical phloem pattern with slight induction by salt stress. pAgMT3 and pAgMaT3 expression was induced by salt stress, except in minor veins. pAgMaT3 was highly active in stressed roots. The promoters described here could be regarded as new tools for engineering salt-resistant plants.

Research highlights
► We investigated gene expression in the phloem of celery plants after long-term salt stress.
► 3 genes studied: 2 encoding metallothioneins (AgMT2/3) and 1 a new mannitol transporter (AgMaT3).
► Promoter/Reporter gene expression confirmed phloem location and stress induction in Arabidopsis.
► Promoters could be used to monitor salt stress responses in the phloem of plants.