LOCALIZATION OF EXPRESSION OF KNAT3, A CLASS-2 KNOTTED1-LIKE GENE

KNAT3 is a class 2 kn1-like gene in Arabidopsis thaliana. The RNA expr ession patterns of KNAT3 were characterized through the use of promote r-GUS fusion analysis and in situ hybridization. KNAT3 is expressed in several tissues and at several times during development. There are th ree main expression patterns: (1) during early organ development in yo ung leaves, buds and pedicels; (2) at and near the junction between tw o organs at specific times during development, including the hypocotyl -root boundary in young seedlings, the anther-filament junction in mat ure flowers, and the ovule-funiculus and peduncle-silique boundaries i n elongating siliques; and (3) in maturing tissues such as the style o f elongating siliques, the petioles of maturing leaves, and most of th e root. The varied expression patterns may indicate that KNAT3 plays s everal different roles in plants, depending on when and where it is ex pressed. Previous work on KNAT3 (Serikawa et al., 1996) indicated that expression of its RNA is regulated by light. Promoter-GUS seedlings w ere grown under different light conditions (continuous white, red and far-red light) to examine more closely the light regulation of the KNA T3 promoter. Continuous white light resulted in stronger overall GUS s taining in the same patterns seen in seedlings grown under long-day co nditions (cotyledons, upper hypocotyl and roots). Continuous red light resulted in reduced GUS expression in those same tissues. Continuous far-red light led to seedlings showing stronger staining in the hypoco tyl and cotyledons than red light-grown plants but no staining in the roots. Thus, the KNAT3 promoter responds differently to red and far-re d light.