Hairy Sheath Research Articles

Cytokinin Promotes Jasmonic Acid Accumulation in the Control of Maize Leaf Growth.

Plant organ growth results from the combined activity of cell division and cell expansion. The co-ordination of these two processes depends on the interplay between multiple hormones that determine the final organ size. Using the semidominant Hairy Sheath Frayed1 (Hsf1) maize mutant that hypersignals the perception of cytokinin (CK), we show that CK can reduce leaf size and growth rate by decreasing cell division. Linked to CK hypersignaling, the Hsf1 mutant has an increased jasmonic acid (JA) content, a hormone that can inhibit cell division. The treatment of wild-type seedlings with exogenous JA reduces maize leaf size and growth rate, while JA-deficient maize mutants have increased leaf size and growth rate. Expression analysis revealed the increased transcript accumulation of several JA pathway genes in the Hsf1 leaf growth zone. A transient treatment of growing wild-type maize shoots with exogenous CK also induced the expression of JA biosynthetic genes, although this effect was blocked by the co-treatment with cycloheximide. Together, our results suggest that CK can promote JA accumulation, possibly through the increased expression of specific JA pathway genes.

The Maize Hairy Sheath Frayed1 (Hsf1) Mutation Alters Leaf Patterning through Increased Cytokinin Signaling.

Leaf morphogenesis requires growth polarized along three axes-proximal-distal (P-D) axis, medial-lateral axis, and abaxial-adaxial axis. Grass leaves display a prominent P-D polarity consisting of a proximal sheath separated from the distal blade by the auricle and ligule. Although proper specification of the four segments is essential for normal morphology, our knowledge is incomplete regarding the mechanisms that influence P-D specification in monocots such as maize (Zea mays). Here, we report the identification of the gene underlying the semidominant, leaf patterning maize mutant Hairy Sheath Frayed1 (Hsf1). Hsf1 plants produce leaves with outgrowths consisting of proximal segments-sheath, auricle, and ligule-emanating from the distal blade margin. Analysis of three independent Hsf1 alleles revealed gain-of-function missense mutations in the ligand binding domain of the maize cytokinin (CK) receptor Z. mays Histidine Kinase1 (ZmHK1) gene. Biochemical analysis and structural modeling suggest the mutated residues near the CK binding pocket affect CK binding affinity. Treatment of the wild-type seedlings with exogenous CK phenocopied the Hsf1 leaf phenotypes. Results from expression and epistatic analyses indicated the Hsf1 mutant receptor appears to be hypersignaling. Our results demonstrate that hypersignaling of CK in incipient leaf primordia can reprogram developmental patterns in maize.

Maize mutants and variants altering developmental time and their heterochronic interactions.

It is useful to envision two fundamentally different ways by which the timing of plant development is regulated: developmental stage-transition mechanisms and time-to-flowering mechanisms. The existence of both mechanisms is indicated by the behavior of various mutants. Shoot stage transitions are defined by dominant mutants representing at least four different genes; each mutant retards transitions from juvenile shoot stages to more adult shoot stages. In addition, dominant leaf stage-transition mutants in at least seven different genes have similar phenotypes, but the leaf rather than the shoot is the focus (and at least two of these genes encode homeodomain proteins.) One mutant, Hairy sheath frayed 1-O (Hsf1-O) simultaneously affects shoot and leaf; this mutant's behavior initiated our interest in plant heterochronism. The second type of timekeeping involves time-to-flowering. As with most plant but not animal species, cultivars of the maize species vary greatly for the time-to-flowering quantitative trait: between 6 and 14 weeks is common. It is via the 'slipping time frames' interaction that takes place between stage-transition mutants and time-to-flowering genetic backgrounds that unexpected and radical phenotypes occur. We see a reservoir of previously unsuspected morphological possibilities among the few heterochronic genotypes we have constructed, possibilities that may mimic the sort of variation needed to fuel macroevolution without having to posit (as done by Goldschmidt) any special macromutational mechanisms.

HAIRY‐SHEATH FRAYED #1‐O: A SYSTEMIC, HETEROCHRONIC MUTANT OF MAIZE THAT SPECIFIES SLOW DEVELOPMENTAL STAGE TRANSITIONS

Hairy sheath frayed‐1 (Hsf1‐O), an ethyl methanesolfonate‐induced dominant mutant in maize, was first described as an excessively hairy plant with pronglike projections of sheath that extended from the margin of the leaf blade. We describe several other phenotypes and show that Hsf1‐O affects virtually every segment of the plant. We have identified genetic backgrounds that suppress some of the Hsf1‐O phenotypes. The morphological descriptions reveal a prolongation of cell differentiation in certain tissues and organs. In general, transformations are from more adult to more juvenile, not older to younger. On the assumption that Hsf1‐O acts with the same developmental logic in both the apical meristem and leaf primordia, the leaf sheath is a juvenile blade, not a young blade. Genetic background effects show that the expressivity of the phenotype is influenced by the plant's time to anthesis. The suppression and temporal shift in Hsf1‐O expression patterns in early flowering lines is due to the inherent accelerated maturation of cells in these lines. In early flowering lines, transformations are suppressed and shifted toward the less mature (younger) tissues, organs, and segments of the plant. We conclude that Hsf1‐O is a heterochronic mutation that prolongs the time to maturity (delays terminal differentiation), and that a primordial cell's developmental maturity rather than the cell's position can dictate that cell's fate. Hsf1‐O disconnects the rate of developmental stage transition from the overall flowering‐time rate.

Hairy-Sheath Frayed # 1-0: A Systemic, Heterochronic Mutant of Maize that Specifies Slow Developmental Stage Transitions

Hairy sheath frayed-1 (Hsf1-O), an ethyl methanesolfonate-induced dominant mutant in maize, was first described as an excessively hairy plant with pronglike projections of sheath that extended from the margin of the leaf blade. We describe several other phenotypes and show that Hsf1-O affects virtually every segment of the plant. We have identified genetic backgrounds that suppress some of the Hsf1-O phenotypes. The morphological descriptions reveal a prolongation of cell differentiation in certain tissues and organs. In general, transformations are from more adult to more juvenile, not older to younger. On the assumption that Hsf1-O acts with the same developmental logic in both the apical meristem and leaf primordia, the leaf sheath is a juvenile blade, not a young blade. Genetic background effects show that the expressivity of the phenotype is influenced by the plant's time to anthesis. The suppression and temporal shift in Hsf1-O expression patterns in early flowering lines is due to the inherent accelerated maturation of cells in these lines. In early flowering lines, transformations are suppressed and shifted toward the less mature (younger) tissues, organs, and segments of the plant. We conclude that Hsf1-O is a heterochronic mutation that prolongs the time to maturity (delays terminal differentiation), and that a primordial cell's developmental maturity rather than the cell's position can dictate that cell's fate. Hsf1-O disconnects the rate of developmental stage transition from the overall flowering-time rate.

The genera <i>Polygonum</i> and <i>Bilderdykia</i> (Polygonaceae) in southern Africa: morphology and taxonomic value of the ocrea and fruit

The external morphology of the fruit and the ocrea of 16 taxa of Polygonum and Bilderdykia in southern Africa was studied.Fruits are either lenticular or trigonous. Six types of fruit surfaces were distinguished. Five types of ocreae were found, characterized by: a green undulating limb; a silvery hyaline sheath; a brown tubular sheath without terminal hairs; a terminal fringe of short cilia or setae; and a bristly hairy sheath fringed with long rigid setae.

Genetics of five hairy phenotypes and a linkage group of Pennisetum americanum

In pearl millet hairy lamina, hairy sheath and hairy stem were inherited as monofactorial recessives while hairy leaf margin and hairy node were inherited as monogenic dominant traits. The gene for hairy lamina hl showed independent assortment from the gene for hairy node, Hn, and showed linkage with the genes hst (hairy stem), hs (hairy sheath) and Hm (hairy leaf margin). Furthermore, Hl was observed to have an epistatic effect on the expression of hs. The percentages of recombination between the gene pairs hl-hst, hl-hs and hl-Hm were 0.0, 8.30±0.44 and 19.81±0.98 respectively. Thus the genes hl-hst-hs Hm form one linkage group.

Isolation of Streptomyces finlayi from the Rhizoplane of Egyptian Clover (Trifolium alexandrinum)

A representative strain (531) of green streptomycetes occurring in the root surface region of Egyptian clover (Trifolium alexandrinum) was identified as a typical strain of Streptomyces finlayi, a species which seems capable of living, in loose protocooperative or commensalistic association, also with soil invertebrates (Szabó 1974). In the aerial mycelium of strain 531, spore-chains both with a typical hairy sheath and without a sheath (smooth spores) were observed. According to our present and previous observations the release of spores after the disruption of the hairy sheath seems to be a frequently occurring phenomenon in the aerial mycelium of many strains of S. finlayi.