Cross-Species Identification of Mendel's I Locus

Abstract

A key gene involved in plant senescence, mutations of which partially disable chlorophyll catabolism and confer stay-green leaf and cotyledon phenotypes, has been identified in Pisum sativum, Arabidopsis thaliana, and Festuca pratensis by using classical and molecular genetics and comparative genomics. A stay-green locus in F. pratensis is syntenically equivalent to a similar stay-green locus on rice chromosome 9. Functional testing in Arabidopsis of a homolog of the rice candidate gene revealed (i) senescence-associated gene expression and (ii) a stay-green phenotype after RNA interference silencing. Genetic mapping in pea demonstrated cosegregation with the yellow/green cotyledon polymorphism (I/i) first reported by Gregor Mendel in 1866.

Stay-green protein, defective in Mendel’s green cotyledon mutant, acts independent and upstream of pheophorbide a oxygenase in the chlorophyll catabolic pathway

“…Recently, the mutation of Mendel's I locus was elucidated molecularly . In contrast to an earlier finding of reduced SGR gene expression in the mutant (Armstead et al, 2007), gene expression was found to be normal. By complementing a rice sgr mutant with rice SGR gene exhibiting a 6-bp-insertion, it was concluded that the analogous mutation present in Mendel's green pea SGR gene abolished SGR function .…”

“…The Columbia (Col-0) ecotype of Arabidopsis (Arabidopsis thaliana) was used as wild type. For silencing of AtSGR1 by RNA interference, a pHannibal-derived construct as described in Armstead et al (2007) was used. pao1 was transformed by a floral dip method and homozygous pao1 atsgr1i lines selected by kanamycin resistance.…”

“…This was possible, since pao1 is not resistant to kanamycin (Alonso et al, 2003;Pružinská et al, 2005). Production of the AtSGR1-silencing lines, atsgr1i, has been described (Armstead et al, 2007). A homozygous AtSGR2 T-DNA insertion line of the SALK collection (Alonso et al, 2003) was obtained from the European Arabidopsis Stock Center, Nottingham, UK.…”

“…By exploiting the high micro synteny between Lolium-Festuca and rice, it was possible to identify the candidate locus in a Lolium stay-green mapping population that corresponded to a stay-green locus (SGR) in rice (Armstead et al, 2006). Silencing of the orthologous gene, AtSGR1 (At4g22920) of Arabidopsis, caused the same stay-greenness as in Festuca or Lolium (Armstead et al, 2007).…”

“…Furthermore, it has been shown that SGR maps to the I locus of Mendel's green cotyledon mutant (Armstead et al, 2007). Thus, the I locus is only the third identified locus of the seven traits Gregor Mendel used for establishing his laws of genetic inheritance (Mendel, 1866).…”