Transcriptional Study of the RsmZ-sRNAs and Their Relationship to the Biosynthesis of Alginate and Alkylresorcinols in Azotobacter vinelandii.

The GacS/A system in Azotobacter vinelandii regulates alginate and alkylresorcinols production through RsmZ1, a small regulatory RNA (sRNA) that releases the translational repression of the algD and arpR mRNAs caused by the RsmA protein. In the Pseudomonadaceae family, the Rsm-sRNAs are grouped into three families: RsmX, RmsY and RsmZ. Besides RsmZ1, A. vinelandii has six other isoforms belonging to the RsmZ family and another one to the RsmY. Environmental signals controlling rsmsRNAs genes in A. vinelandii are unknown. In this work, we present a transcriptional study of the A. vinelandii rsmZ1-7-sRNAs genes, whose transcriptional profiles showed a differential expression pattern, but all of them exhibited their maximal expression at the stationary growth phase. Furthermore, we found that succinate promoted higher expression levels of all the rsmZ1-7 genes compared to glycolytic carbon sources. Single mutants of the rsmZ-sRNAs family were constructed and their impact on alginate production was assessed. We did not observe correlation between the alginate phenotype of each rsmZ-sRNA mutant and the expression level of the corresponding sRNA, which suggests the existence of additional factors affecting their impact on alginate production. Similar results were found in the regulation exerted by the RsmZ-sRNAs on alkylresorcinol synthesis.

Salt stress in Thellungiella halophila activates Na+ transport mechanisms required for salinity tolerance.

Salinity is considered one of the major limiting factors for plant growth and agricultural productivity. We are using salt cress (Thellungiella halophila) to identify biochemical mechanisms that enable plants to grow in saline conditions. Under salt stress, the major site of Na+ accumulation occurred in old leaves, followed by young leaves and taproots, with the least accumulation occurring in lateral roots. Salt treatment increased both the H+ transport and hydrolytic activity of salt cress tonoplast (TP) and plasma membrane (PM) H(+)-ATPases from leaves and roots. TP Na(+)/H+ exchange was greatly stimulated by growth of the plants in NaCl, both in leaves and roots. Expression of the PM H(+)-ATPase isoform AHA3, the Na+ transporter HKT1, and the Na(+)/H+ exchanger SOS1 were examined in PMs isolated from control and salt-treated salt cress roots and leaves. An increased expression of SOS1, but no changes in levels of AHA3 and HKT1, was observed. NHX1 was only detected in PM fractions of roots, and a salt-induced increase in protein expression was observed. Analysis of the levels of expression of vacuolar H(+)-translocating ATPase subunits showed no major changes in protein expression of subunits VHA-A or VHA-B with salt treatment; however, VHA-E showed an increased expression in leaf tissue, but not in roots, when the plants were treated with NaCl. Salt cress plants were able to distribute and store Na+ by a very strict control of ion movement across both the TP and PM.