Cold Acclimation-induced Changes in Gene Expression in Roots and Crown Buds

2Dept. of Agronomy and Range Science, University of California, Davis, CA 95616-8515

Alfalfa improvement programs would benefit by understanding mechanisms controlling fall dormancy and winter survival. Our objectives are to identify and characterize genes associated with fall dormancy reaction and winter survival of alfalfa. Selections from ‘CUF-101’ (fall nondormant) for greater fall dormancy produced plants with reduced herbage growth in autumn and markedly improved winterhardiness (Table 1).

We used differential display to analyze root and bud tissues for transcript differences between CUF 101 and CUF 101-L, the population selected for increased fall dormancy. Northern and dot-blot analyses to date have confirmed cold acclimation-responsive (CAR) cDNA clones that are differentially expressed between CUF 101 and CUF 101-L. The mRNA levels for certain CAR cDNAs were about 10-fold more abundant in December in CUF 101-L which survived winter when compared to CUF 101 (Fig 1).

CUF 101			Norseman
L	O	H	L	O	H

Figure 1. Northern analysis showing differential expression of CAR genes in alfalfa roots in December. See Table 1 for germplasm descriptions.

Nucleotide sequence analyses of two of our CAR cDNA clones showed high homology to previous identified cold-acclimation-specific cDNAs (cas15A and cas15B) from alfalfa (Laberge et al., 1993; Monroy et al., 1993). Our results suggest we have cloned new members of the cas15 gene family that are highly expressed during hardening of fall dormant alfalfa. Expression of these CAR genes is positively associated with winter survival. We have cloned full-length cDNAs for several of our CAR genes. We are currently analyzing the deduced amino acid sequences for to elucidate their function. We plan to transform the nonhardy CUF 101 and other nondormant cultivars with constructs containing these CAR genes to determine their impact on winter survival and fall dormancy.