Far-red light-insensitive, phytochrome A-deficient mutants of tomato

Abstract

We have selected two recessive mutants of tomato with slightly longer hypocotyls than the wild type, one under low fluence rate (3 mumol/m2/s) red light (R) and the other under low fluence rate blue light. These two mutants were shown to be allelic and further analysis revealed that hypocotyl growth was totally insensitive to far-red light (FR). We propose the gene symbol fri (far-red light insensitive) for this locus and have mapped it on chromosome 10. Immunochemically detectable phytochrome A polypeptide is essentially absent in the fri mutants as is the bulk spectrophotometrically detectable labile phytochrome pool in etiolated seedlings. A phytochrome B-like polypeptide is present in normal amounts and a small stable phytochrome pool can be readily detected by spectrophotometry in the fri mutants. Inhibition of hypocotyl growth by a R pulse given every 4 h is quantitatively similar in the fri mutants and wild type and the effect is to a large extent reversible if R pulses are followed immediately by a FR pulse. After 7 days in darkness, both fri mutants and the wild type become green on transfer to white light, but after 7 days in FR, the wild-type seedlings that have expanded their cotyledons lose their capacity to green in white light, while the fri mutants de-etiolate. Adult plants of the fri mutants show retarded growth and are prone to wilting, but exhibit a normal elongation response to FR given at the end of the daily photoperiod. The inhibition of seed germination by continuous FR exhibited by the wild type is normal in the fri mutants.(ABSTRACT TRUNCATED AT 250 WORDS)

Photomorphogenesis and phyfohormones

“…The 2-to 3-fold higher IAA content of the mutants was associated with in vitro morphogenic development characteristic of a high IAAicytokinin ratio. The preliminary results we have obtained using well-characterized phyA {fri) and phyBl {tri) mutants of tomato, and the corresponding double mutant (Van Tuinen et al 1995;Kerckhoffs et al 1996), appear to confirm the previous data, indicating involvement of both phytochromes A and Bl in regulation of the IAA level. Taken together, these results strongly suggest involvement of a light-induced decrease in IAA level in the light inhibition of plant cell elongation.…”

Function of Phytochrome A in Potato Plants as Revealed through the Study of Transgenic Plants

“…Thus, phyA is involved in sensing R, which indicates that even under continuous R-sufficient Pfr molecules remain available to mediate the response. The relative insensitivity of phyA antisense sprouts to R contrasts with results obtained with phyA-deficient Arabidopsis and tomato plants (Nagatani et al, 1993;Reed et al, 1994;van Tuinen et al, 1995). After 5 d of continuous growth in R, the length of wt potato sprouts was reduced to 20% of the leve1 of sprouts grown in the dark, whereas the sprout length of antisense plants reached 80% of the value of dark-grown controls.…”

“…Under continuous R, hypocotyls of wt Arabidopsis seedlings reached 37% of the length of the dark-grown controls, whereas seedlings of a pkyA mutant reached 54% (Reed et al, 1994). R-mediated inhibition of hypocotyl elongation of wt tomato seedlings led to seedlings reaching 23% of the size of dark-grown seedlings, whereas phyA-deficient seedlings were slightly less inhibited (32%; van Tuinen et al, 1995). Taken together, these data reveal that in the etiolated stage potato phyA mediates a considerably larger component of the response to R than is observed in Arabidopsis and tomato.…”

The phytochrome gene family in tomato (Solarium lycopersicum L.)

“…Van Tuinen et al (1995a) selected two mutants, with slightly elongated hypocotyls under red and blue light, respectively. The two mutants were subsequently found to be allelic and, as for the PHYA mutants of Arabidopsis (Whitelam & Harberd 1994), insensitive as seedlings to far-red light.…”