Subfunctionalization of PhyB1 and PhyB2 in the control of seedling and mature plant traits in maize

Abstract

SummaryPhytochromes are the primary red/far-red photoreceptors of higher plants, mediating numerous developmental processes throughout the life cycle, from germination to flowering. In seed plants, phytochromes are encoded by a small gene family with each member performing both distinct and redundant roles in mediating physiological responses to light cues. Studies in both eudicot and monocot species have defined a central role for phytochrome B in mediating responses to light in the control of several agronomically important traits, including plant height, transitions to flowering and axillary branch meristem development. Here we characterize Mutator-induced alleles of PhyB1 and a naturally occurring deletion allele of PhyB2 in Zea mays (maize). Using single and double mutants, we show that the highly similar PhyB1 and PhyB2 genes encode proteins with both overlapping and non-redundant functions that control seedling and mature plant traits. PHYB1 and PHYB2 regulate elongation of sheath and stem tissues of mature plants and contribute to the lightmediated regulation of PhyA and Cab gene transcripts. However, PHYB1 and not PHYB2 contributes significantly to the inhibition of mesocotyl elongation under red light, whereas PHYB2 and to a lesser extent PHYB1 mediate the photoperiod-dependent floral transition. This sub functionalization of PHYB activities in maize has probably occurred since the tetraploidization of maize, and may contribute to flowering time variation in modern-day varieties.

The genetic architecture of leaf number and its genetic relationship to flowering time in maize

“…Upregulating and downregulating ZCN8 mRNA also causes changes in leaf number. Comparative genomics and mutant analyses have identified several other flowering time genes in maize (Sheehan et al ., 2007; Danilevskaya et al ., 2008; Miller et al ., 2008; Dong et al ., 2012). …”

Evolutionary Studies Illuminate the Structural-Functional Model of Plant Phytochromes

“…each photoreceptor, although few data are available to test the conservation of gene function in seed plants other than Arabidopsis. Nonetheless, the available data from Brassica, cucumber (Cucumis sativus), pea (Pisum sativum), tobacco (Nicotiana tabacum), tomato (Solanum lycopersicum), maize (Zea mays), and rice (Oryza sativa) suggest that the functions of phyA and phyB are generally conserved and were established prior to the split of eudicots and monocots (Ballaré et al, 1991;Childs et al, 1991;Devlin et al, 1992;Weller et al, 2004;Sheehan et al, 2007;Takano et al, 2005Takano et al, , 2009, although independently duplicated phyB may subdivide functions differently than is seen in Arabidopsis phyB and phyD (e.g., Hudson et al, 1997;Kerckhoffs et al, 1999;Weller et al, 2000;Sheehan et al, 2007). Functional data from dicots that diverge deeper than the eudicot/monocot split in the angiosperm phylogenetic tree are needed to infer that their functions are conserved in all angiosperms, but this is a reasonable hypothesis.…”

Physiological and Genetic Characterization of End-of-Day Far-Red Light Response in Maize Seedlings

“…Mutations at phyB1 and phyB2 also impair light signal transduction. At maturity, both PHYB1 and PHYB2 contribute to plant height, stem diameter, and sheath-internode length, but PHYB2 predominates in the control of flowering (Sheehan et al, 2007). Like the sorghum and rice phyB mutants (Childs et al, 1997;Takano et al, 2005;Kebrom et al, 2010), both elm1 and phyB1 phyB2 double mutants constitutively display several traits associated with low R:FR response (Sawers et al, 2002;Markelz et al, 2003;Sheehan et al, 2007).…”

“…In maize, an ancient alloploidization has doubled the family size to six: PhyA1, PhyA2, PhyB1, PhyB2, PhyC1, and PhyC2 (Sheehan et al, 2004). Although many similarities are apparent between maize and Arabidopsis (Arabidopsis thaliana) light response, there are significant differences between members of the phytochrome gene family in copy number and selection pressures that have resulted in the divergence of phytochrome signaling networks (Sawers et al, 2005;Sheehan et al, 2007). Thus far, only three phytochrome mutants have been characterized in maize: elongated mesocotyl1 (elm1), phyB1, and phyB2.…”