Enhancing salt and drought tolerance of <i>Poa</i> and triploid <i>Cynodon</i> with <i>BADH</i> gene and somaclonal variation
Triploid bermudagrass (Cynodon dactylon × C. transvaalensis) and Kentucky bluegrass (Poa pratensis L.) are popular warm and cool-season turfgrasses, respectively. The clonal property of these two species makes them good targets for biotechnological improvement. The first transformation system for triploid bermudagrass was established using biolistic bombardment. Embryogenic callus was induced from stolons. Using the hpt gene as the selectable marker gene, 75 transgenic lines were obtained from 18 petri dishes bombarded. Homogeneously transformed plants showing stable transcription of the hpt gene were confirmed. An efficient transformation system of elite cultivars of Kentucky bluegrass was also established. Embryogenic callus was induced from mature seeds. Efficient transformation systems of triploid bermudagrass and Kentucky bluegrass provide realistic possibilities for their biotechnological improvement.
The BADH gene from Atriplex hortensis, an enzyme in betaine synthesis, was transformed into triplod bermudagrass, cv. ‘TifEagle’, and Kentucky bluegrass, cv. ‘Langara’, respectively. Three of 32 transgenic bermudagrass lines that contained the BADH gene showed significant improvement for drought tolerance. Four of 43 transgenic Kentucky bluegrass lines that contained the BADH gene showed significant improvement for salt tolerance. One of these 4 lines also showed better drought tolerance.
BADH activity assay indicated all transgenic lines with improved tolerance had higher BADH activity, ranging from 3.0 to 19.8 unit/mg protein, significantly higher than that of the controls. Assays showed that leaf osmolalities of all these transgenic lines were approximately 100 mM higher than that of the controls. These results indicate that stress tolerance of triploid bermudagrasses and Kentucky bluegrasses could be improved through constitutive expression of the BADH gene.
A lack of superior Kentucky bluegrass salt tolerant germplasm has largely delayed the genetic improvement of salt tolerance of elite cultivars. Through somaclonal variation, 40 variant cell lines of Kentucky bluegrass (cv. ‘Shamrock’) that grew stably on medium supplemented with 0.7% NaCl were selected. Eleven regeneration lines showed significant improvement for salt tolerance at the 1.0–1.2% NaCl concentration. Ten of these 11 lines also showed significant improvements for drought tolerance. These results indicate that somaclonal variation promises to be a useful method in abiotic stress tolerance improvement of Kentucky bluegrass.